If you want easy, then go with the infinite NES lives boards. You flash them with a programmer that is available on the site. The only thing you'll need to solder is a battery clip, though he may do that for you if you ask.
If you want a board with the ability to do a LOT more, then the boards on Mortoff games are the way to go. But, you'll need to solder and be able to program EPROMs (27C322 and/or 27C160).
Just wait on the N64 stuff, seriously. I haven't used the retrostage boards, but I've been made well aware of s number of flaws that they have. It's not really a shock to me, considering all the other boards I've purchased from that site are just awful quality, and those don't even include logic. If you can't get a bare PCB board right, then it's hard to imagine a fully populated flash memory board from the same fellow being any good.