What denominations are similar to Baptists?

Historically the Congregationalists would be closest. Both grew out of English Puritans and Dissenters. Baptists were influenced by some Dissenter refugee contact with Anabaptists in the Netherlands, however, and came to embrace distinctive doctrines and practices from other English Puritans.

Justin A. Smith.. editor of the Chicago Standard a long time ago.. said of Baptist succession..

"The sum of all this is, that whether or not a succession of Baptist churches can, as some think, be traced through centuries of the Middle Ages down to the time when our denominational history in its strict sense begins, we may at least say that our ancestry goes upward along a line of descent in which, if any where in the world, pure Christianity survived; and that among our Baptist progenitors, in this sense, were men and women who had the conspicuous honor to be maligned by those when history proves to have been adepts in the two trades of murder and slander (Smith, Modern Church History, 227)" From A History of the Baptists by John T.Christian, 1922.

JohnB445 said:

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It's been 4 years since I've been a believer. I have studied many denominations, I don't know which one I will be. But so far Baptist doctrine sounds not only the most peaceful and comforting, but it makes the most sense to me. But maybe I might switch denominations because I still haven't really looked at another denominations.

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Depends on the Baptist doctrine. Not all Baptists, for instance, hold to "once saved always saved" and double down on the belief that people have a choice (ex. Free Will and General Baptists). For that matter, some of the tenets of Calvinism, such as predestination, are not universally embraced by Southern Baptists.
If you lean more to the Free Will side (the OP suggests though that you don't), the Church of God-Anderson, IN (Anderson is the group's HQ, they have congregations across the US) is very similar to Baptists.

FireDragon76 said:

Historically the Congregationalists would be closest. Both grew out of English Puritans and Dissenters. Baptists were influenced by some Dissenter refugee contact with Anabaptists in the Netherlands, however, and came to embrace distinctive doctrines and practices from other English Puritans.

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However, the majority of modern Congregationalists are extremely progressive in Biblical interpretation, with most Congregationalist churches having been absorbed into the United Church of Christ in 1957.

actionsub said:

However, the majority of modern Congregationalists are extremely progressive in Biblical interpretation, with most Congregationalist churches having been absorbed into the United Church of Christ in 1957.

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The liberal/progressive reputation of the UCC is due mostly to the fact that some of the congregations in the Northeast dual-affiliate with Unitarian Universalists. Non-UU affiliated congregations are going to be more like other Mainline Protestant bodies.

FireDragon76 said:

The liberal/progressive reputation of the UCC is due mostly to the fact that some of the congregations in the Northeast dual-affiliate with Unitarian Universalists. Non-UU affiliated congregations are going to be more like other Mainline Protestant bodies.

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As a former UCC seminarian, that progressivism runs very deep. (Full disclosure: most of the UCC churches where I live in the Midwest trace their lineage to German immigrants who were part of the old Prussian Union in Europe. Even those old German churches are fairly progressive in doctrine and practice.) While there are similarities, there are no "dual-aligned" UCC congregations that I know of. Part of this is because the Unitarians functionally split the old Congregational Church in the early 1800s.
Progressivism is integral to UCC identity, and the progressive party line is pushed very hard in their seminaries, even the non-Congregationalist ones. Trust me on this. That said, a running joke is that UCC stands for "Universalists Considering Christ".
The UUA and the UCC have collaborated on a sexuality curriculum called "Our Whole Lives", and there are talks between the two denoms regarding future collaboration. If there was future dual alignment, it would not surprise me much.
There are two other major Congregationalist denominations: the NACCC and the CCCC. The NACCC is not quite as progressive as the UCC; they maintain a more centrist theological stance in line with the majority of mainline churches. The main issue with the NACCC was polity; they felt a merger with the presbyterial church government of the E&R churches.
The CCCC is the conservative side of Congregationalism and the smallest of the three. Their issues were both theological and social; they sought to maintain a more creedally-informed doctrinal stance along with opposition to abortion, LGBTQ marriage, and ordination of same-sex oriented individuals.

actionsub said:

As a former UCC seminarian, that progressivism runs very deep. (Full disclosure: most of the UCC churches where I live in the Midwest trace their lineage to German immigrants who were part of the old Prussian Union in Europe. Even those old German churches are fairly progressive in doctrine and practice.) While there are similarities, there are no "dual-aligned" UCC congregations that I know of. Part of this is because the Unitarians functionally split the old Congregational Church in the early 1800s.

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There is an element of truth in this: John Nevin and Philip Schaff's religion was a kind of modernist "Reformed Catholicism", whereas the bulk of Presbyterians at the time were toying with a kind of proto-fundamentalism and revivalism.

It's also noteworthy that most European churches are also relatively liberal. In Europe, what we think of as a "conservative" church, the French often call un culte ("a cult").

actionsub said:

Progressivism is integral to UCC identity, and the progressive party line is pushed very hard in their seminaries, even the non-Congregationalist ones. Trust me on this. That said, a running joke is that UCC stands for "Universalists Considering Christ".

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That's funny because it's probably closer to the truth for me than I think for the local UCC congregation, who just seem like socially progressive Evangelical Pietists.

In Australia it seems like the Baptist Church and the Church of Christ had common origins. I was informed that there was some sort of split in the church and, I think, the Church of Christ broke away from the Baptists but I have been unable to find out what caused that split. They must have been similiar enough so that when my Grandparents, and their children, moved from Warnambool to Geelong and could not find a Church Of Christ anywhere nearby they began to fellowship at the local Baptist Church. Subsequently my parents continued in the Baptist church and raised myself and siblings as Baptists.

Is the Great Commission Collective another Baptist denomination?

FireDragon76 said:

the local UCC congregation, who just seem like socially progressive Evangelical Pietists.

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And you, sir, have just described the UCC in a nutshell!

Andrewn said:

Is the Great Commission Collective another Baptist denomination?

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It appears to be a network of sorts within the Southern Baptists.

actionsub said:

And you, sir, have just described the UCC in a nutshell!

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What I mean is once you get past the liberal social values, many aren't that different from other American Evangelicals in terms of what they actually believe and do.

Actual adherence to liberal theology seems somewhat exaggerated. It's more like just a liberal broad church, sort of like Anglicans or Episcopalians, that just happens to have congregationalist polity.