The Cen is still pretty new and I have only seen one at our local track, a buddy of mine just picked up one. I havn't had a chance to take a close look yet so no opinion there. I have seen the HB's come and go at our local tracks and they never seen to do very well and the owners don't seem to keep them very long either. I'll let you read what you want into that!
Party wagon made some good suggestions as well here about going to your local track and finding out what guys are running there. Like he said the track owner might be able to point you in the right direction in finding a good used ride. When it comes to buying used with anything I have a motto I keep and that is if I can't see or touch it I won't buy it. I have seen a few buds get burned buying used off of places like E-Bay and such. Take your time and do your homework and you will be happier in the end and enjoy the hobby to it's fullest.