Me too, I am running a TW ROM on my SGS2. There are some things that TW still does better than stock Android certainly, but nothing I can't live without.
The problem with TW ROMs is that leaves you completely dependent on Samsung to release updates. Currently my SGS2 is on 4.1, and if I get the 4.2 update it will probably be the last one. Every CM version for the device has needed Samsung to release the kernel source code to work properly, so when Samsung decides the device no longer get updates it no longer gets updates.
For my SGS2 this dead-end isn't a big deal because I want a new phone anyway with a better screen and faster SoC. That sort of dead end will matter much more with a SGS4, where its screen and SoC are powerful enough that I should be able to get three years out of the device instead of 18 months. Without CM I might get stuck on older TW ROMs at the two year mark which will make the phone less useful to me.
As it is I prefer TW ROMs, but I would take a mostly working CM ROM of the newest version of Android any day over a TW ROM of an Android two releases ago.
Basically I want a Nexus without the crappy hardware. I think the US SGS4 should give me that.