Every market is going to have multiple players (Pepsi vs Coke, Microsoft vs Apple, Goldman Sachs vs Fidelity, Google vs Yahoo); competition is healthy and usually indicative of a solid market. While there may be some heat between YC and TechStars because of the Application Form, they're both great additions to the Venture Capital Field.
Both teams have great members and mentors; PG being at the top of the list for YC, Brad Feld being up there for TS. An aspiring serial entrepreneur will do well to learn and be accepted by either company, of that I'm sure.
I'd have to say that currently Y is considered a "brand" now with Mike constantly mentioning the companies on his blog, Y with a strong community, and PG was the first to introduce this concept.
However,if an entrepreneur had the honor of being accepted into either Techstars or Y Combinator, I'm sure he/she would work their butt off not only for themselves but to represent the program he/she is in. Multiple players foster a very healthy competition.
We'll just have to wait and see which program selects the better "animal" entrepreneurs for this round. The success of a startup involves not only the people heading it, but a large part depends on the entrepreneur themselves and the ability to implement or create something useful. How very exciting!
Both teams have great members and mentors; PG being at the top of the list for YC, Brad Feld being up there for TS. An aspiring serial entrepreneur will do well to learn and be accepted by either company, of that I'm sure.