I only own the MSX versions, and never played any other versions, so can't really compare either.
First of all the first 4 games are
on cartridge, so no loading times at all, which is great. The last two are on micro floppy disks.
Also the MSX2 had a rather rich colour palette for an 8-bit machine, so I think the colours of most of the games on it usually look really vibrant compared to other systems, and the Dragon Slayer games (apart maybe from the first) are no exception.
- Dragon Slayer 1 looks very rudimentary graphically (your char is a stick man basically) and sounds very basic too; looks like an early MSX1 game (which it basically was).
- Xanadu looks A LOT better. Makes good use of the aforementioned much richer colour palette of the MSX2. Scrolling is choppy, which was a typical MSX problem that only got solved with the MSX2+. As said, I can't compare with other versions, but the MSX version of Xanadu has only a small window where the action takes place. Most of the screen is filled with the HUD.
- Romancia looks a bit worse than Xanadu imo, but the image is not scrolling. You move from screen to screen, so it's a smoother experience in that department.
- Drasle Family looks and sounds great. Not the prettiest MSX game out there, but nevertheless very nice. You also move from screen to screen.
- Sorcerian I have yet to play.
- Legend of Heroes is on 5 micro floppies (a Program disk, a User disk and 3 Scenario disks). You have to switch between them, which is kind of annoying. Also every battle has to be loaded first, fortunately the loading time is a matter of a few seconds. The game looks very good though. One of the prettier games on MSX I've played. Also the sound is very good. I own an MSX2+, so I'm assuming it uses the built-in MSX Music chip. I could test it on an MSX2 as well to see the difference, but haven't bothered doing that yet.