Best experience of my life.
Biggest difference between YC and TS (from what I hear) is that TS spends much more time hands-on mentoring.
I had the honor to have ~60 1on1 meetings with very respectable entrepreneurs and investors during the program. In addition to very high quality workshops and inspiring talks almost every day. Compare that to the weekly office hours at YC (again, through multiple grapevine branches).
I personally deem the TS experience the most accelerating for my personal career, as well as our start-up.
I wrote about my experience and my lessons learned here: http://www.techstars.com/content/accelerators/lessons-busine...
I have heard mixed stories from other Techstars chapters, especially the corporate sponsored ones. But I can vouch for Chicago :)