I think if you look at the production figures, you'll find that there were a whole pile more Type 38s built. After all, the thing was in production from 1905, right through to 1945. The Type 99 dates only from 1939.
I have a Type 38 and thing is just scary accurate if you feed it the right stuff. Of course, it had been around when I got it; it was given to me by a dealer in order to "raise the quality of his junk rack". I took it home, drained the oil, steamed out close to 100 dents in the wood, glass-bedded the thing, scraped the crud out of the bore and it shot under a nickel at 145 yards.... and there was even an actual witness there to see it. It loves Norma factory ammo.
The Jap 7.7 rifle cartridge, basically, is a rimless .303: more horsepower but not the control you have with the light-recoiling 6.5x50.5SR round.
Either one is a piece of history, especially if you get one that hasn't had the chrysanthemum ground off.
A friend has one in .30-'06, a Thai rebuild, of course.
A bunch were also rebuilt in Indonesia, marked with a 5-pointed star; they also did Lee-Enfields with the same marking.
If you're REALLY lucky, you MIGHT run into one of the Siamese contract Arisakas from the 1920s. They were in an 8x58Rimmed that you have to make out of .45-70USG and they are awfully scarce, or so it seems. The later Thai rebuilds to that calibre are comparatively plentiful, but many of them have been used to make .45-70s from. I weep, verily!
Whatever model you get, just be sure to have fun with it.