I've seen both the HP and Gateway monitors before...not bad. What's your budget for monitors?
If you can afford the Gateway, definately go for it. It's VERY nicely built, has 4 USB ports and supports DVI, VGA, S-Video, Composite and HD-Composite.
It's also height adjustable and can turn 90 degrees for a portrait look. The HP is also very nice, but I don't really like the bezel...looks too much like a TV with the monitors on the side. But that's just my complaint, so it really depends on yours.
Either way, both of these monitors are very nice and are well worth the money. If I were to pick one, I'd go with the Gateway. It supports a slew of inputs, is HD ready, has 4 USB ports, height-adjustable and has VERY, VERY solid construction. I've seen both up close, and I'll tell you one thing...you won't be disappointed with either monitor.