You'll find that many folks on this board are fans of both, with a slight bit more using the Apeks.
I dive the Zeagle version of the Apeks TX50, known as the Tech 50D, and I love it. I purchased it upon the recommendation of one of the local tech diving guru's after a good discussion of what I wanted to do for my first year or two diving, and what I wanted to do in my 5th and 7th year of diving (penetrating sunken wrecks, going into caverns, and other techie stuff). The Apeks and Zeagle regs are good choices for that type of diving.
As far as comfort, with the correct length hose, and the Seacure mouthpiece, the Tech50D literally dissappears and the only reason I know it's there is because it's feeding me air and my breathing sounds "mechanical" and Darth Vader-ish. The second stage is fully adjustable and it breaths very easily both shallow and at 90 feet. And the exahust ports work well diverting the bubbles away from my field of vision.
So the Apeks and Zeagle lines are ones that I definitely encourage first time purchasers to investigate. They are a high quality product, and one that you will not outgrow during your dive career unless you get into heavy technical stuff. They are well made and are backed up by strong warranty programs.
Prices on the Apeks TX50's are running around $350 on LeisurePro.com (but please see past arguments/discussions about purchasing life supoort equipment online vs. local shops) to $450-500 at some shops. But again, it's well worth the investment.
The only experience I have had with the Mares is picking one up at the dive shop while waiting my turn with the clerk. So I will have to pass the soapbox off to someone who owns one.
