I wouldn't go for the Luna, it is a legacy computer that needs a inferred dongle to be able to connect it to a PC. I would consider the G2 or the newest, and less expensive, the A2. Both the G2 and the A2 can work as AI with SP's transmitter.
Considering the "algorithm" issue, it is of TOTAL irrelevance to the recreational diver at all levels. The algorithm that SP uses is very configurable and you can customize it including disabling some of the optional adjustments it has. I have used it with other computers from other vendors and it correlated to "middle of the road" results in terms of its conservatism. The RGBM based recreational computers from Suunto, Mares, Cressi, etc. are more conservative computers that penalize you for several profiles by locking you out for the following dive when the SP doesn't. SP's computers are solid and have excellent reputation and are used worldwide. I also have friends who are technical divers and some are technical diving instructors who have been using the SP dive computers since the G dive computer in their technical diving and have no issues with it at all.