Well, and if you're looking for your own best tank, there are some other questions than 'what's popular?'
Ask: 1) what do you want most---fish or corals. If you ache to have a tang, and are in the market for a tank, consult the list for tang tanks in the newbie forum. You want a Long tank, at least 4 feet (48"), and to get a 75, you'll need to go more shallow. This may limit you a bit on corals, if you want those too. For angels, you're kind of on your own right now: nobody's even considered how to spell out what they need---but if you take tangs as an example of the most extreme fast-moving fish we keep in tanks, angels won't be unhappy in what fits them: consider adult size, etc.
2. lighting: fancy colored stick corals take extreme light, and it's easier to light a High or deep tank rather than a Long---the longer you go, the more fixtures you have to buy. An 8 foot reef is a thing of beauty, but lighting it and getting flow to go nicely is quite a job. I light my corner 54g with 1 bulb. A Long would have taken 2. An 8 footer---just about 4 bulbs. With metal halide---that'll cost a mint!
It's not just about gallons. It's about use.
Does that help?