I'm quoteing myself from another post I made about the Polks. This is in reference to the different RTi series speakers. This is also assuming that you'll be running a sub.
The RTi8s have the best balanced driver configuration for being paired with a sub (IMO). The RTi8s have 2 6.5" drivers, the 10s have 1 6.5" and 2 7" drivers, and the 12's have 2 5.25" and 3 7" drivers. When mated with a sub and crossed over at 80hz, you really aren't going to be needing those 7" drivers. Also, the RTi8s have 2 6.5" for your mid-range, whereas the 10s only have one, and the 12s only have 2 5.25" drivers. So, when mated with a sub, the RTi8s are going to be the best match, and just happen to be the cheapest of the 3!
If you aren't using a sub, then I'd go for the 12s, since I like to feel my music as well as listen to it. Having a sub really makes the difference though. Hope this helps.
