Look, everyone's going to say get a bigger tank, but that doesn't mean you should do it. If you want a 75, get it! What you might want to ask yourself is what kind of tank inhabitants do you want? What kind of fish, corals, etc...

For a reef with a lot of stony corals that need strong water movement and light, the "double cube" shape or some variation on it is terrific. It's easy to light and circulate water, and the aquascaping is terrific on this shape tank. The main thing is that the height and width (front to back) are about the same. This means 15 gal (24X12X12), 45 breeder 36X18X16tall) 120 gal (48X24X24) etc... make really nice reef tanks. In this case, the 75 is probably better. If you're looking at a 48" tank, and you want bigger than the 75, I'd go to the 120 rather than the 90 (extra width rather than height) if you're wanting to build a reef.

As far as brands go, Oceanic is the standard; but you must buy their stand to get the 5 year warranty. Aqua trends build decent tanks; they're local, so if it leaks you can get it fixed pretty easily. Compare prices on those two and you can decide. I went with aquatrends because I already had a nice stand, and i did not want to pay oceanic prices without the warranty. Sure enough, my aquatrends tank had a problem, but they replaced the tank. It didn't cost me, but it was a REAL PITA to take everything out and get the new tank in there.