All I’ve dealt with up to this point is the Printrboard controllers (on my PBJr and Simple). What’s the overall best “separate bits” controller board/stepper motor board/etc combo out there, otherwise? I want to gradually source and build a Prusa i3.
The printrboard is my favorite that’s what I’m using on my prusa i2
RAMBo is the best board out there. Not the cheapest, but no issues with hardware, very expandable and service is the best
The RAMPS is one of the most used boards out there and can be expanded in whichever way you want. It’s also one of the cheapest ways to control a printer, with a an Arduino Mega clone, the RAMPS and four drivers starting at around $60.
@J_O11 , the RAMBo doesn’t use upgradable/replacable motor drivers. One of those blows up, your screwed. That’s what OP is trying to get away from.
My suggestion is Arduino MEGA + RAMPS; as you can get it awesomely cheap from http://sainsmart.com with or without drivers, so you can decide if you want to go with the A4988s, or the DRV8825s which are relatively new, but much better.
Yes, the Rambo doesn’t have replaceable drivers, but I’ve shipped WELL over 1,000 with our various kits/machines and I have yet to see one that has ever had a blown driver. Can’t say the same for any pluggable style driver board I’ve ever used.
That is seriously something you should disclose. You’re financially “obligated” to push the RAMBo…please make that clear next time. It’s clear to me that you don’t care that the OP mentioned he wanted a board with separate drivers, as long as you got to push your product. I get that you also have had the most experience with this product, and will naturally gravitate toward suggesting it because of that, but you ignored the OPs primary request and it looks a little shady.
@ThantiK , While ‘I’ am not financially obligated to push the RAMBo (they are made by UltiMachine, not me), the OP did say ‘otherwise’ after the seperate bits comment, and I, having used more options than most, thought I would comment on what is the most reliable board out there. UltiMachine is the original designer of RAMPS, and RAMBo is their newest board. Anything RAMPS related is a clone of their original work, with in most cases no design improvement, and also in most cases much less stability. Don’t think i was ‘pushing’ my wares on here man, just posting a very well meant comment on what many would agree is the solid choice. Don’t believe me, ask Prusa what he uses on all his i3’s now 
The RAMBo is nice, just way out of my (desired) price range! Thanks for the suggestions, everyone. I ended up going with another Printrboard, from Makerfarm. It will replace the pending-replacement controller on my PBSimple, and then when the replacement arrives I’ll use that on my next 'bot.