I have to say that I too have tried them all and TP is the one that answers my questions accurately and quickly every time. If it's Europe I like to use inyoupocket.com which is really good an allows you to print out your own travel guides on various European cities. Unfortunately the site is in its infancy and the locations are limited but still growing. Hope this helps.
I have to agree with nearly everyone and say I definitely prefer to use Travellerspoint.
I do use Thorntree but have also been called an ignorant aussie and just about everything else under the sun (and btw been accused of not knowing the difference between Greece and Turkey but I actually hadn't mentioned Turkey at all... go figure). People on TT totally abused this elderly lady once because she said she didn't want to walk anywhere... vermin's.
The only thing missing here is some hard core India fans! I posted a question and mostly got spam, it seems SE Asia takes preference here in the Asia forum, but I also go on India Mike for tidbits or just the old lonely planet guide book. I have only travelled in south India but once I finish my 6 week trip to north india I'll be happy to share my knowledge (as small as it may be).