Hi Paloma: I’m not sure what the price difference is. I would not recommend the Trek Lexa (sora) only because it’s a 9 speed bike and most new bikes nowadays are 11-speed, and it would be impossible to upgrade down the line. Also, I read that the Sora shift levers on the handlebar are not adjustable unlike 105 and so there are some complaints that the levers are hard to reach with smaller hands. Further, it may not make any sense to you, but the gear ratios changes too much between gear and would make for a less enjoyable ride. But it may be worthwhile to buy it if you plan on training/racing with it for 1-2 years, and then using it as a commuter, then upgrading to something better.
105 is the best bang for the buck universally. It feels great, will last you for many many years, and has good resale value. The Cannondale Synapse 105 is awesome and won Bike of the Year in 2014 and 2015. I would get one myself if I didn’t already own two road bikes. The Liv Avail SL looks pretty good too and seems to have good reviews online. So I would choose between Synapse and Avail, and base your primary decision on price and fit. I know color is important too for some people…..:) Synapse is probably more expensive because of the awards that it has won, but I would consider both bikes as equals.
I recommend asking the local bike shops about the pros and cons of both. They probably know more than me.
