A 40 breeder is probably your easiest to maintain tank with the greatest number of options for types of fish, while a 55 is going to offer more variety with a slightly more difficult amount of maintenance.
Personally, I keep a few 20 longs. It limits my stocking options, but I'm currently renting and my landlord doesn't mind these. When I get around to buying a home, I'll likely switch out the 3 20Ls for 2 75s.
I know what you're thinking; "I asked about fish, not aquariums."
That's the thing. While I applaud you researching fish and looking for what the fish you like require, it's absolutely tortuous to yourself to get your heart set on a fish you won't be able to accommodate.
Figure out what you can have first. If you're placing your aquarium on a second floor, you're likely not going to be able to safely go bigger than a 55. If you're a renter, you may not be able to keep an aquarium at all, or you may have to pay a deposit and/or increased rent. If you're incredibly fortunate, you may have a landlord that allows small aquariums, like I do.
Once you work that out, then you'll be able to look at options and work from there. The smallest aquarium I recommend for a new fishkeeper is a 20 gallon long. It supports a surprising number of different fish because it has the same footprint as a 29 gallon. The list of species it shares with the latter is so large, in fact, that the only options you really gain from there are Angelfish and a couple of the larger Gourami. From there I'd jump to a 40 breeder or a 55.
My point is, figure out how big you can go in the area you have designated,
then start looking at fish. When it comes to tank size, bigger is always better, as it will give you more options. Starting with a small tank isn't necessarily bad, either. When you're ready to move on past that 20L, you can use it as a
Quarantine Tank for your 75.
You don't want to get your heart set on a beautiful
Pearl Gourami that you're not currently able to properly home and just have to look at them wistfully every time you're at the LFS.
...not that I would know what that's like.