Tough one. I personally don't think an auto can top a revolver if reliability means firing the round every time the trigger is pulled. Both designs are susceptible to mechanical failures. However, the revolver gives an advantage if the failure is with the ammunition. Bad primer, or whatever, you can simply pull the trigger again with the revolver. It's simply not as quick or simple with the auto. I think everybody knows this...
That said, I have a J frame in .38 and a PM9.
Reliability is a funny thing... I have about 1,000 rounds through the PM9 and it worked every time. Is it reliable? I don't know... at a minimum it's consistent and I trust it to fire the chambered round every time. From that perspective I would rely on it as much as I would the J frame.
There are two main differences I want to note. One, the PM9 holds 7 or 8 rounds (depending on which mag I use) of 9mm and two, it reloads faster.
When I look at the practical difference the question of reliability becomes a little more clear. 5 rounds should be enough... it really should. However, when I "practice" scenario shoots I find that I dump 4 or 5 rounds WAY faster than I realize and end up clicking the revolver when I should still be shooting. I try to make it as real as possible... and I run out of ammo more often than not. That's not going to reliably save my life.
The 7/8 round count on the PM9 gives enough rounds to take on two targets in my drills and gives me a fast reload if needed. That's where I feel like it trumps the snub .38. 14 total rounds including the reload vs 5 and no hope of reload (I just can't manage a speed loader for the snub).
So, given the above, I rely on the PM9 more than I rely on the .38 to get me out of a bad situation. For me, I would argue the PM9 is more reliable. I would argue that same way for any other auto that generally functions properly.