In my opinion Telco customizations are leading to a whole bigger problem as they maybe don't have the infrastructure to keep on top of the required updates for all of their supported phones.
Back to the OP if it were me in your position I would (and yes i am a biased SGS2 owner :P) I would look towards getting an S2 for the following reasons;
* Out of the box it is a great experience lacking nothing in usability
* It is one of the favourite androids at there at present and the unofficial support network is collectively spending crazy amounts of time and effort tinkering which is leading to a number of great custom rom's if you want to go down the tweaker's track, there are vanilla AOSP roms, tweaked samsung factory roms all the way through to heavily themed roms that plain scare me :P
* SGS2 has officially been announced for Ice Cream Sandwich 4.0 upgrade sometime next year, this means that there will be factory support and upgrade paths made available without the potential issues of tweaking unofficially
Sometimes you are better off buying the latest version of an older model than you are buying an unproven brand new freshly released model