They will all be very much the same at that price. I will say that the carbon fork does matter though, if you can get one with a carbon fork go for that one. I vote for the Allez out of those choices you listed. There are other choices though that will fit in your budget. Do you have a performnace bike near you? Here is a nice bike with a carbon fork and Tiagra 10 speed for $799

http://www.performancebike.com/bikes...400315__400315

This one is equiped one 105 for just $100 more

http://www.performancebike.com/bikes...400315__400315