The Legend is a very well made first stage although definitely I prefer the Adjustable LX second stages. Functionally speaking the Legend LX Supreme is virtually identical to the Apeks XTX200. If it were me, I'd buy the Legend LX Supreme for a variety of reasons.
Aqualung owns Apeks so dealer wise there is little difference - except that while all Aqualung dealers sell Aqualung regs, not all Aqualung dealers sell and stock parts for Apeks regs, so service is potentially slower to obtain on an Apeks reg.
With a smaller company like Salvo, Dive-Rite, Atomic, Zeagle, etc, service can get extremely interesting if you relocate to another part of the country or need service while you are on a dive trip. Both Aqualug and Scubapro have very wide ranging worldwide dealer networks and you can get service virtually anywhere. Plus it's a safe bet that Aqualung and Scubapro will both be around in 10 years and that they will still support and service a reg that you buy today. Other companies? I would not bet on it.
As for buying on-line, it's your decision, but the hidden costs, warranty problems, service issues and general ill will it breeds with the LDS you depend on for air far outstrips the upfront savings in very short order.