I don't have any problem with walls of JABBA barrels and Z-Fighting - as long as you've upgraded to the current latest. Factorization barrels, on the other hand, are a killer.
I'll admit I don't use the FTB Launcher, but I do keep a fair sized pack, originally transposed from an older FTB pack into Magic Launcher to manage it easier, and I've only ever had one major issue with Optifine - it didn't like Biomes O Plenty. However, with the latest back-ported 1.6.4 versions he's made, the problem has gone away.
The only other issue, which is really very minor, is that some things cease to be rendered if the centre of them is no longer on the screen. SGCraft and Lantea Stargates, for example, only render if the bottom-base block is visible to me. But since I rarely, if ever, have anything of the sort, I barely ever notice it.
FPS++ is a suitable alternative if you're really so annoyingly set on banishing Optifine. It doesn't offer quite as much IMO - I like the more finely grained control Optifine offers, and if Forge would take a leaf from him and implement that themselves, I'd happily drop it.
And, if you can get FPS++ to work, and you still find the need, simply drop the Optifine JAR into your mods folder, and FPS++ will load it. I believe Optifine is actually made to be loadable from the mods folder by FML recently too.
In short, I think if you actually read the changelogs, he's started to take note of the compatibility concerns and do something about them - so don't just knock it because you had bad experiences with it before.