Cyclocross - Ultegra or 105?

Which component group is better or preferred? Reference to Ultegra on Cannondale Cyclocross Disc or 105 on Specialized Tricross. Also, what's the general mood toward disc brakes?

There's not really much difference between Ultegra and 105. Ultegra usually has a slightly better finish, but functionally I think they are almost identical. I'd probably err toward the Cannondale since Cannondale make great frames. Make sure that you are looking at the whole spec though. A common wheeze is to fit an Ultegra rear mech on an otherwise 105 bike, or fit a cheap and gnasty crank to an otherwise ok bike. Wheels are often sacrificed too. Buy based on the frame and it's suitability to your intended purposes.

ultegra will be a little bit lighter, but other than that no big differences. they will, for all practical purposes, feel the same.

Buy the 105. Easy to upgrade if you ever desire. The frame and fork are much more difficult to change.

Ultegra brifters and hubs are better than 105, the other groupe items are more equel.

I vote 105. If you are racing and are going to be dragging the whole lot through mud on a weekly basis come September then you might as well save the money when it comes time to replace something. That said, my 105 RD, FD, and brifters have lasted 4 years of racing and year-round commuting without a hitch, knock on wood.

Not a huge difference between 105 and Ultegra... I'd let fit fit and quality of the frame/fork be my main determinants.

I have a disc-equipped CX bike and love the Avid BB7's. Powerful and easy to adjust. Basically unaffected by mud and water. If those things matter to you, you'll love them, too.

You should know that if you plan to race at a high level that discs are illegal per the UCI. If not I think they are the best choice for the job. The only downside is weight.