I got myself an MSX last year, so I have some thoughts to share.
The first thing is going to be what you want to use it for (presumably games). The big divisions in MSX hardware are:
MSX (original) - very primitive in its graphical and musical capabilities but has a large and strong selection of software. If you want to collect legit copies of games, they're usually on cartridges which are a lot more reliable than 30+ year old floppy disks you'd get for later MSX.
MSX2 - a big upgrade, this will let you play MANY more games than the original MSX. If you want to play Metal Gear, you'll need an MSX2
MSX2+ - minor upgrade from the regular MSX2, not as widely supported as MSX2, but the upgrades do make it pretty nice.
MSX TurboR - only made by Panasonic, very few games have TurboR enhancements, but it's very nice. If you want to shell out big bucks for the best of the best, a TurboR is probably the way to go.
The MSX built-in character set is different depending on the region it was released. So if you want to play Japanese games, Japanese text will appear garbled on an MSX with an international character set. And of course if you want to play European games, lowercase letters will appear as garbled Japanese on a machine with a Japanese character set. I haven't really explored fan-translations so I'm not sure how compatible they tend to be on actual hardware. If you live in America and import an MSX from Europe, you'll have the added headache of dealing with different voltage and PAL-video output. And if you live in Europe and want a Japanese TurboR, you'll have the headache of different voltage and NTSC-video. And if you have an MSX that's capable of RGB-video output, I'm not sure how easy it would be to get that connected to modern display. And then there's the fact that the power supply will likely have failing capacitors that you'll want to replace ASAP. The world of vintage computers can be a headache, especially when you get into importing things from different continents.
The specific model I got was a Yamaha CX5MII/128, which was released in the US. It has a built-in MIDI-compatible FM synthesizer and I really liked the idea of having an 8-bit computer that I can use for music. Plus it has more RAM than almost any other pre-MSX2 model and two cartridge slots. Being able to play Japanese games is just a bonus! I only have on cartridge (Kitten's Adventure) but without a controller, it's very difficult to play.
What do you want from your MSX? Emulating might be the best option TBH. There's also the extremely cool-looking
MSXVR - I haven't looked into it too deeply, but if you don't want to mess with ancient PCs and don't want to just emulate it in Windows, it's another very viable (though expensive) option.
Anyway, it's hard to pick a "best" without knowing your specific interest. I'm not an expert but I can try to answer whatever questions as best as I can.