The OPC split from the liberal Northern Presbyterian Church in the mid 1930s. The PCA split when the Northern and Southern churches merged in the early 1970's.
The merged church, PC(USA) is very liberal and dying on the vine. They are the ones ordaining homosexuals.
From a doctrinal perspective, conservative Presbyterians, all hold to the Westminister Confession. The OPC and PCA differ in the way they evolved over time, having spit from liberal bodies at different times and in different parts of the country.
The ARP allows women to serve as deacons, but not elders or teaching elders. The PCA and OPC don't. I don't know enough about the RPCNA to comment.
What does this mean to "everyday" Presbyterians? Members can move between the OPC and PCA, as well as the ARP with no problem. Pastors can as well.
I have been a member of the PCA, ARP as well as the United Reformed Church of North America (which is Dutch Reformed). The URCNA holds to some documents called the Three Forms of Unity and when I joined I could not distinguish between them and Presbyterian doctrine. I have actually been in several Presbyterian Churches that use Question One of the Heidelberg Catechism, a Reformed Church document, for responsive reading.
Q. What is your only comfort in life and in death?A. That I am not my own,1 but belong— body and soul, in life and in death—2 to my faithful Savior, Jesus Christ.3 He has fully paid for all my sins with his precious blood,4 and has set me free from the tyranny of the devil.5 He also watches over me in such a way6 that not a hair can fall from my head without the will of my Father in heaven;7 in fact, all things must work together for my salvation.8 Because I belong to him, Christ, by his Holy Spirit, assures me of eternal life9 and makes me wholeheartedly willing and ready from now on to live for him.10
1 1 Cor. 6:19-20
2 Rom. 14:7-9
3 1 Cor. 3:23; Titus 2:14
4 1 Pet. 1:18-19; 1 John 1:7-9; 2:2
5 John 8:34-36; Heb. 2:14-15; 1 John 3:1-11
6 John 6:39-40; 10:27-30; 2 Thess. 3:3; 1 Pet. 1:5
7 Matt. 10:29-31; Luke 21:16-18
8 Rom. 8:28
9 Rom. 8:15-16; 2 Cor. 1:21-22; 5:5; Eph. 1:13-14
10 Rom. 8:1-17
Here is one article: Differences between the OPC and the PCA that may help.
PAR35 may be able to provide some insight as to the accuracy of the link, as well as my above blatherings.
Both ARP and RPCNA are NAPARC members, as are the PCA and OPC, and the URCNA. (and several others not mentioned here) http://www.naparc.org/member-churches/
While there are stylistic and substantive differences within NAPARC, they are considered to be in full communion, with fairly easy movement between the denominations. The Presbyterian members subscribe to the Westminster Standards (Some more tightly than others). (The Reformed members subscribed to the Three Forms of Unity).
The PCA is the largest of the NAPARC denominations, the most aggressive in church planting and missions (although many of the smaller members ‘punch above their weight’) and probably has the most problems.
To get to specifics - It is my understanding that both the RPCNA and the ARP ordain women as Deacons. The biggest difference is probably what is seen as acceptable music in worship. Any attempt at full merger at this point would lead to a split.
Other Presbyterian denominations you may have heard of (there are several dozen at this point) are the Evangelical Presbyterian Church (subscribes to the Westminster standards, but has women ordained to all offices) Evangelical Covenant Order (laundry list of Confessions - anyone should be able to find something to agree with) liberal in all but one respect - they won’t ordain practicing homosexuals. and the PCUSA - pretty much anything goes at this point, no longer Presbyterian in governance.
Generally any NAPARC church should be safe as to doctrine (there are are few PCA congregations I’d be concerned about), a few EPC that I’d recommend if there wasn’t anything better within an hour or so drive, and ECO and PCUSA should be avoided at all costs.