They are quite different computers. The Vyper is a large "Puck" style computer where as the Oceanic is a watch style. If you want to wear the computer as a day to day watch then go with the Geo. If you want flexibility in the way you mount your computer there are lots of different mounts available for the Vyper from Suunto and others.
Common wisdom is that Suunto computers run a more conservative algorithm (RGBM) than Oceanic (mod-Haldanean). Some will say a more liberal computer gives you more diving and can be made more conservative if you want, but not vica-versa. In practical terms you are only likely to find the Suunto limiting your diving versus the Oceanic if you are doing four or more dives a day beyond 15m/30min.
Given that there is no decompression model that accurately models ALL the factors involved in inert gas loading/unloading, sensible diving practices (slow ascents, safety stops, good general fitness, mid-week breaks on diving holidays, appropriate exposure protection, adequate hydration, conservative use of nitrox, not exercising or drinking alcohol after diving) will make a bigger difference to your safety than the specific algorithm you go for.
What may in fact be more important to you is what algorithms the computers of the people you dive with run. That way you will end up with the same stops/no-stop times and are all singing from the same hymn sheet, so to speak. As a general rule all computers within a manufacture's contemporary range will run similar or at least compatible algorithms.
I Personally have a Vyper and would whole heartedly recommend them to anyone, purely on an ease of use/functionality point. I have not used the new Geo so can't really comment but... the Vyper has a "Plan" function which according to the Oceanic website the Geo doesn't. This function lets you see roughly how much no-stop time you would have on your next dive, based on your previous dives and surface intervals.
No matter what computer you buy, it cannot and will not guarantee you never take a hit. Every year I see one or two divers who've taken a hit on dives shallower than 10m and shorter than 30min.
