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Unfortunately, the only computer I have had the opportunity to use has always been the Suunto Zoop as it is the most common rented computer here. Due to this I do not have first hand experience with a variety of computers. There are some great suggestions here which I will most definitely have a look at.
Leonardo and probably Mares should not be that different from Zoop in how they calculate your bottom time. Where the differences between them and "non-RGBM" computers begin to add up is multi-day multi dive trips, particulariy with liveaboard-type schedules. If you plan on doing that sort of thing, that would be an argument against Zoop/Leo/Puck.
The puck pro is great. A very simple one button setup that after a quick tutorial is easy to navigate and hard to go wrong. The alarm and ascent rate visuals are straight forward. A great choice for someone who wants to keep things simple.
Something that you will find useful if you choose to go for a second hand is this:Buy a mid-level pre-owned dive computer. There are lots of great computers at budget prices that will do the basics for you. Then in a few years, with lots of diving, you can get your ideal computer.
Leonardo and probably Mares should not be that different from Zoop in how they calculate your bottom time. Where the differences between them and "non-RGBM" computers begin to add up is multi-day multi dive trips, particulariy with liveaboard-type schedules. If you plan on doing that sort of thing, that would be an argument against Zoop/Leo/Puck.
Suunto have taken a bashing in recent years for poor quality control and really poor warranty handling, particularly with pressure sensors - so there are a lot of people who got burned by that and would never buy Suunto again.