I'm going to chime in on this thread. I only read the first page, so there's that.
Anyway, there is no 'best' sword art. Context is key, but since context is relatively meaningless in a modern landscape, it's more about what you're looking for. If you're just looking for something to be good at, then anything will do. I would make judgments based solely on aesthetics. If you're looking for something good for historical combat, I recommend HEMA (essentially history fencing, not modern fencing), or a koryu style of kenjutsu.
Mostly, this is going to boil down to what's available to you. Colorado, where I live, is bigger than a lot of other states as far as fencing or Asian sword fighting styles go, and even then there's only 2-3 HEMA clubs in the entire state, and then you have tons of kendo which don't realistically emulate historical combat. There do, of course, exist koryu swords arts, but they're largely in the Denver area. I'm not sure if this is a trend that persists in other states -- non-sport combative arts being located in metro areas that might be too far to attend.
What kendo will teach you is maai, which in European fencing is called 'measure.' This is the time, distance, and angles of striking (or line) between two people. If you've studied unarmed martial arts, you probably have some familiarity with measure.
The difference between HEMA and kendo is that in most HEMA clubs, you'll readily have access to historically accurate reproduction weapons that have a full-blade forte and rolled tips (as well as polypropylene weapons), whereas you'll mostly be using shinai/ bokken if studying kendo. Both are fine, but studying exclusively on shinai doesn't teach you proper edge alignment, weight of a sword, weight distribution, and general bad habits with handling real swords in regards to blade integrity, ect. Bokken do have orientation for this, but every place is different. Even then, bokken aren't an entirely accurate representation of katana, just like how a waster isn't an entirely accurate representation of a longsword.
If you manage to find a koryu kenjutsu place (unlikely), then it boils down to if you have a preference for European weapons (many HEMA clubs delve into fencing other than with a sword, such as polearms) or Japanese swords (since you've specifically stated in the OP that you have an interest for learning swordsmanship). It's unlikely that you'll find any Chinese or Korean places that practice with swords considering how saturated the market is with Japanese-centrism.
Personally, I've been doing kenjutsu for a long time and have always been interested in historical fencing, have picked up things here and there, but over the last year-and-a-half have devoted more time towards reading manuscripts and manuals, and I find it enjoyable. As far as modern fencing (never having done it myself), I've seen a lot of techniques that are more about getting points before the other person using techniques and strategies that would more or less be liable to kill both people if you fought that way in a real duel. That's just my speculation.