Both are good computers.
I've got the Genesis React Pro. It works very good and has never given me any trouble. However, if I had to buy again, I wouldn't buy it. You have to press buttons on it underwater to get all your readings (like max depth, etc) as they are on "secondary screens". I would buy a computer that has everything you need on a dive on one screen.
The Suunto Gekko is a good computer too. But it's very conservative most folks will say. One of the things I don't like about it is that when you start your 3 minute saftey stop at 20 feet, if you drop below 20 feet it will re-start the 3 minute timer. It also restarts it if you go above so many feet. So if you're hanging on a bouncing anchor line that is going up and down, it's frustrating to get in the 'right spot' to do your 3 minutes. Suunto is also distributed by the "evil Aqualung empire" where they force "list price" sales on their dealers. I would rather not give my money to their empire.
If I had over to buy my Genesis React Pro again, I'd prob choose something like the TUSA IQ-700 or maybe an Oceanic. The IQ-700 has a LARGE screen with all dive info on one screen while you are diving. It also supports two gas mixes which is good for deep diving where you might change to a stage bottle or pony bottle or use the regulator some boat operators have at the 20 foot bar. "Gas 2" on it also will go up to 100% o2 if you were using it for deco on pure o2.
Just my thoughts on the two computers you asked about and what I might do if I had to do it over again. While my choice now wouldn't be for either of the two you listed, neither of those two are bad computers (and I even own one of them).
BTW.. if your shop doesn't carry computer I mentioned, Dive Rite makes the same computer with their logo on it and charges a few buck more (list price) for it. I'm sure if your shop would let you have the Dive Rite one for the Tusa price (if they carried Dive Rite).
hope all that helps.
-mike