I prefer the Gen4 grip(without additional backstraps) and magazine release, but I wouldn't want to deal with the possible problems it may have being a 9mm Gen4. Most Gen4 9mm's work flawlessly, but a rather high number of people have failures to eject with theirs. Some have fixed theirs by replacing the guide rod with the latest factory guide rod, others by using an aftermarket guide rod or adaptor that allows use of a Gen3 guide rod, others by replacing the extractor, and a few people haven't been able to get theirs to work reliably. Even Glock doesn't seem to understand what the problem is with the Gen4 9mm models.
The other caliber Gen4's don't have any problems. Though with Glock's newest extractors, no matter which Generation Glock you buy, you may get an extractor that's too tight. Some people just replace the extractor with another factory one, other people polish the top and bottom surfaces of the extractor, others get an aftermarket extractor made by Lone Wolf Distributors. My Gen3 G27 with a test-fire date in late 2009 had one of the new extractors and was ejecting a few cases straight up over my head, plus about 90% of the cases were scraped up pretty badly. I replaced it with a LWD extractor but I haven't had a chance to test it with that extractor yet.
I'd personally get the RTF2. It's a Gen3, just with a different grip texture and possibly scallop-shaped slide serrations. It may still have a tight extractor, but that's the only thing to worry about as with any new production Glock. You may find the texture too aggressive, it feels fine to me.