I've had all three.
GT Omega, was a pain to put together as the screw holes DO NOT line up for the back and front, I had to get my dad to twist it into the right position while I forced the screws in. Every time you moved it would make a noise like metal hitting metal, nothing was the matter just the mechanism on the bottom just wasn't working correctly. The arm's where also very stiff and would only move if I forced them. Stitching was decent but a few off peices where it wasnt lined up right. Also the recline wasn't smooth it was in notches which you could really feel. It went back for a full refund, they paid for pick up.
AK Racing (I got the premium one), pretty nice, was simple enough to put together and looks the business. However, again the mechanism on the bottom was making noises when moving like metal hitting middle, and the side pieces which cover the connecting mechanism are just awful, they are not designed for the chair, are made of very cheap and thin plastic, mind decided to just snap of while I was at work, one of the sides on the floor with a hole in it. Stitching was great though and the recline was decent enough....Sent it back.
DX racer (I have DXRACER OH/DF51/NW), went together perfectly, everything lines up, stitching is great, padding is great, and NO noise what so ever when moving, smooth motion of the back recline with no noise. My only quibble is the arm rests (seems to be a common issue with these types of arm rests) are wobbly, but its the design of the rests so can't really complain.
Overall for the money GT Omega is not worth it too many issues
AK racing is worth it as long as you can put up with lackluster quality.
DX racer is VERY worth it.