When Carmen Wong Ulrich's "On The Money" was on weekdays on CNBC, she and her guests used to say that it was a toss-up over the long term, but that you never know how government will change the rules down the road.
General recommendation was to put money in Roth if you are just starting out and anticipate higher earnings power going forward, but later on (when income has stabilized) use standard tax deductible 401k because you just don't know what Congress will do when they need to find more money (just like Elbryn mentions above)
edit: one other thing to research before you make your decision is what specific mutual fund options you have in your 401k. During the panic of last fall and early this year, basically everything was on sale, irrespective of quality of company or stock. Many value and contrarian growth mutual fund investors were able to load up on really high quality companies and place their bets, so to speak, for the next 5 years. Even though many of these funds have already run up 20% this year, there still may be a lot of latent value to be released over at least a 5 year time horizon (when economy has truly recovered and started to grow steadily again). Check out most recent quarterly reports (second quarter commentary may have just been released and may or may not be on websites yet) for your mutual funds and see what they say about anticipated returns going forward. You can also get Morningstar analysis with premium membership (I think there is a 30 free trial available). If all of your mutual fund choices are poor, perhaps paying taxes now makes sense; if you have high quality choices with say 20% per annum potential anticipated returns over next 5 years (as some fund letters were projecting during first quarter of this year or end of last year - I forgot where I read that, but I think I read it in at least two different mutual fund quarterly reports), deferring taxes and deploying that saved money into more 401k mutual fund shares may make more sense. Good luck!