Saitek because its the most inexpensive.
Chess clocks

That's like asking "what's the best opening?" How much money are you willing to spend? Do you want a clock that's user-friendly or isn't that important to you? How many features/options do you need or want?
Chronos clocks are swell and expensive, but there seems to be some question about whether or not the mfr is still in business. I've got a much cheaper Saitek which works, but is 100% user-unfriendly. Try searching the forums here, I've seen several recently about chess clocks and chronos in particular.
And learn how to use search engines, no offense intended which I mention because several assholes here have been mortally offended that anyone dare suggest they try looking something up themself instead of depending on strangers to do all their research for them, even though SAs can often find you better answers faster than waiting for answers in a forum. In the meantime check out these links:
http://www.bizrate.com/games-puzzles/chess-clock/
http://www.chess.com/equipment/chess+clocks
http://reviews.ebay.com/Chess-clocks-and-timers-Which-one-is-right-for-you?ugid=10000000002153690
www.cln.org/searching_faqs.html
What is the best kind of chess clock?