That's going to be a hard one for people to answer. We don't know what size you have space to keep, nor what size you're *inclined* to keep. Saltwater, IMO, is more of an investment in time, cost, and effort (assuming you don't have your own RODI setup, for example) than freshwater, but the fish are generally much prettier.
The same rule of thumb for tank sizing applies to both fresh and salt: the larger the tank, the more room for error. When a small tank starts having water quality issues, it goes downhill fast. My 10 gallon betta tank had a shrimp death, and in hours (2 shrimp at bed time, 1 and a shrimp tail right before lunch), ammonia was at 1.0 or so. Fortunately, I was home, and noticed odd behavior from some tetras that are in with him. On my 55, that would have been a much smaller spike, just due to sheer water volume. And that volume packs much more beneficial bacteria, so it may have evened out before I noticed.
The better question is what do *you* think you're capable of and willing to handle? Then, some advice can be given. Unfortunately, I'm not really a saltwater guy, I just admire them and have learned a few things through observation. I can even answer some hardware questions, but stocking, especially corals, I won't go near. I just lack the familiarity.
Looking at some recent activity, it looks like the people I'd be inclined to lean on for information haven't been on in a few days. Be patient, and they'll come by and will happily advise.
Personally, I'd go in decreasing preference for tank size (again, pending on what you're wanting to deal with and only referencing fairly standard sizing) 75>40 breeder, 29, 55, 20 long, 10. Bowfronts are nice options, and there are some biocubes that are fairly non-standard in size, but may fit your needs. I think some of those even come with built in sumps, which not only filter, but being that they also hold water, they help give you a larger body of water, so parameters won't swing as wildly.