a cheap one. If I'm doing the interviewing, I need to know you are not going to blow the money. If I'm the interviewee and I need to impress you with my watch, I probably wouldn't want to work there. I rather impress you with my "knowledge" of watches.
Once, I impressed in an interview with my knowledge of guns and bullet calibers. That got me a nice offer.
Oh man - not a really watch expert, but lately I've been simping for the Rolex Cellini Moonphase. However, as stunning as it is it's price point is a bit higher than what I am willing to blow for a watch. I'd also guess that with the discontinuation of PP's Nautilus they're bound to become a more prestigious and desired timepiece over time (which is really the only reason why you'd spend that much on a wristwatch). In any case, in my mind it's not even good looking and the only PP that I would ever consider buying is a Grand Complications.
Any ways, all of the above are likely too much of a watch for a quant interview (would make sense though for other kind of interviews).
On the more "affordable" side, the below are my personal preferences:
Omega Speedmaster - I think it's a bit of a must have for every man who's building a collection
Tag Heuer Carrera Chronograph - they have about a million iterations, but I specifically like this one
Ferro & Co came up with the Le Mans not too long ago - it's a beautiful watch, a little unique in the sense it only has one hand, and it's also really cheap (relatively speaking)
Speedmaster is pretty huge and thick though, it's not for everyone. I guess it's the downside of having small wrists, I've taken a liking to a couple of watches from seeing pics on the internet (Omega, Grand Seiko) only to find that they look oversized on my wrist.