AquaLung Leg3nd Elite - $899.00
AquaLung Leg3nd Octopus - $250 (second stage is different than the elite)
Total Cost - $1149.00
Atomic ST1 - $999.00
Atomic Ti2 Otopus - $349.00
Total Cost - $1348.00
Apeks XTX200 - $799.00
Apeks XTX50 Octopus - $270 (same as the XTX200 second stage but has a different face plate)
Total Cost - $1069.00
Personally, if the AquaLung was the front runner, I would choose Apeks instead. It's essentially the same regulator with a different apperance. Since Apeks is part of the AquaLung group, the regulator qualifies for the Parts for Life Program, so service cost should be near identical. If you plan on going tech and into doubles, the ST1 provides better hose routing, but so does the less expensive Apeks XTX50.
The ST1 is a beautiful regulator (yup seen it in person). Price wise though, the M1 or the B2 represent better value than the ST1. In regards to performance, all these regulators breathe the same. You would need a machine to discern any difference. Choose based on ergonomics, hose routing, cost of service, price point and appearance (we have to look good underwater, right?).
Apeks > AquaLung > Atomic. All breathe the same, but you can get the Apeks at a better price point than the other two. If you do decide to use double backmounted tanks, you can install a 5th port into your XTX200 and still be cheaper than the ST1.