At this time it's REALLY easy to buy a genuinely competitive 1/12 chassis and almost impossible to buy a "bad" one. Once you get beyond the T-bar vs. link chassis they all really become variations on the theme. From there it just becomes personal choice, trying a few different chassis to find the one YOU think suits you best.
To start with, find out what the "wheels" at your local track are running. If you have someone there you can get set-up info from you'll be ahead of the game.
A BRIEF listing of some likely candidates (there are many more equally as good):
These first two are the most "different" of the bunch, running the batteries fore and aft rather than across the chassis as is standard practice. This moves the overall weight bias a little bit to the front and seems to help (me, anyway) with on-power steering by reducing push.
See the Darkside Motorsports Mx2 at: http://www.darksidems.com/viewproducts.php?partnum=411
(my personal favorite).
See the Diggity Design 3D12 at: http://www.diggitydesigns.com/3d12_fullkit.html
Of course, when people are talking about "link cars" they're usually talking about the ubiquitous CRC chassis. After years refining their excellent Carpet Knife series they released their all-new Gen-X. The most noteworthy feature is an all-new front end that receives mixed reviews. Some rave about them, others (myself included) rave AT them.
See the CRC Gen-X at: http://www.teamcrc.com/crc/modules.php?name=Shopping_Cart&file=category&categ ory_id=11
Then there are a few EXCELLENT T-bar designs out from these vendors:
See the OD Design OD12 at: http://www.od12.com/products.htm
did very well at the paved Nats this last weekend.
See the BMI DB12 at: http://www.bmiracing.com/
is JUST now coming out in production form. A non-traditional "T-bar", Jason's stuff is ALWAYS top-shelf.
See the PRC Quad 12 at: http://www.powellracingcomponents.com/
A good design as well...probably the best quality carbon fiber I've seen.
See the IRS Rug Rat at: http://www.teamirsrc.com/12scale.html
A very good car, but afaik a conversion kit only. That said, I think you can get everything you need to complete a car. Regardless which chassis you get you need a set of IRS rear height adjusters.
See the Team Laje SpeedEvil 2007 at:http://www.laje.se/index.php?display=products
Has been doing very well in Europe. I know a couple "names" here were going to get them but haven't heard any results. They're a bit pricey, especially since the dollar tanked against the world, but they come completely assembled. I'm going to order a couple of their front end assemblies to try.
And, believe it or not, there are many others. Even the venerable old RC12L4 still wins races. The kits are inexpensive but you really need to figure on at least buying lowered side plates which right away gets the price up into the neighborhood of some of these specialist chassis builders.