Which SSD would you recommend? If a SATAIII disk will work fine in my MBP, I would prefer to buy a SATAIII so that I can use in my next MBP.
One more thought:
Unless a SATA III is close in price to a SATA II so that the price difference isn't a big deal I'd go with a SATA II for several reasons:
1)You probably won't notice any differences in real world use - even though the throughput can be 2X as fast; unless you are maxing out data transfer for large files you won't really benefit from a faster throughput rate.
2) By the time you get a new Mac (assuming at least a year) - SATA III drives will have gotten cheaper - and you'll probably want more capacity by then anyway.
3) Assuming you ell or give away the old MBP - A SSD will add some value if you sell it; if you give it away you'll probably wind up leaving it in anyway if it's for a family member or good friend.
I faced the same choice and went with a 256gb refurb SATA II because the price was very compelling (bout $250). I found the speed increase to be significant enough that I am quite happy with its performance in everyday use (IT takes longer to enter my password than to boot, programs pop one with no bounces), so should I decide to keep it, it will still work in a new MBP at a fraction of the cost of a similar SATA III drive.