Although a small computer sounds great, those that I know that use them, have all upgraded or wished for a larger screen. A puck sized computer is just about right. Of course OLED is the easiest to read in all circumstances.
As to alarms...others will hate you if you set them off often. Your ears should tell you if you are descending or ascending. Make sure what ever you get has the option to turn the alarms off without too much hassle, as you yourself may get tired of hearing them.
I agree with "small" being undesirable. And I recommend not looking to use a dive computer as an everyday watch. I had a buddy on a dive boat who had a ScubaPro, which looked like a sport watch, and without great uncorrected vision, I found the display too small. I agree with "puck" size as being the best for a small computer.
I don't agree with ears telling you when you're ascending. Mine generally don't. And when descending, they only tell me occasionally once I am below 20 feet. The only way I started to learn to tell that I was ascending too fast (
i.e., more than 30 fpm) was with my computer beeping at me. Awareness of ascent and descent may be old hat to old hands, but newer divers need help.
As for recommendations, the usual suspects in the entry-level computer field are Suunto Zoop, Mares Puck (or the more expensive Puck Pro), and, to a lesser extent, Cressi Leonardo. These are in the $190 to $250 range, depending on the make.
I did a review of the Zoop in the following thread, which also had some follow-on posts about the Puck and the Leonardo.
http://www.scubaboard.com/forums/co...s-analyzers/476179-my-review-suunto-zoop.html
For $500, you could get a more advanced computer, such as one that allows gas-switching during a dive, but the models referred to above will handle air and nitrox to 50%.
