None of them are optimal but you got to work with what you have. Tipsarevic is better at playing the "all-out" tennis needed to win.
It's not about "best competition" as in who loses the prettiest. It's about winning the title. Neither of Tipsy or Ferrer probably had the tools to go all the way but with Ferrer he's tried so many times and failed horribly.
Tipsy you can at least give the benefit of doubt. He hasn't had that many chances deep in major tournaments
Ferrer has been in the last 16 of countless slams without even 1 final....do the math
What benefit of a doubt that he will never reach far in slam and will choke. Tipsy is to up and down to compete against either Djoko/Del Potro, at the very least Ferrer will force those two to play great tennis to beat him.