I went with 9 mm and couldn't be happier. Got a CK Arms Thunder Open, and did the "buy once, cry once" on some MBX magazines, and now I got a gun that runs 100% even with cheap factory minor ammo.
If I'm suddenly at like 95%+ at Nationals I'll give serious consideration to the 38 and experiment to see which is "better", but for now I'm more than happy with a gun that runs and having the money and ammo to train all I want.