I recently purchased a 2016 TCR Adv SL2. I can't say enough about the handling characteristics and comfort of this bike. While shopping, I also had a chance to test ride the shop owners 2017 Propel SL 1. Both are amazing bikes. Both are incredibly stable at speed and corner as well or better than any bike I've ever ridden. The TCR was easier to climb with compared to my 2013 Defy Adv 1 as it is about 5 lbs lighter and a bunch stiffer.

I found the TCR a bit more comfortable and decided give up the aero advantage of the Propel for a little bit more comfort. I will say that the 2017 Propel is less buzzy than earlier models. The carbon clincher SLR wheelset on both bikes is also impressive and I have no plans to upgrade.

Lots of riders bag on the ISP, but I have to say that I think the ISP, frame layup and carbon wheels make for a ride quality you wouldn't expect from a full on race bike.

Also, I've had 10 spine surgeries, including a 3 level lumbar and a 3 level cervical fusion and I've had no gripes from my spine on the TCR, even with a 9.5 cm saddle to bar drop. (yes, I do stretch a lot.)

Good luck. I don't think you can go wrong with either bike, as you might have guessed from my review.