All great mathematicians have (basically by definition) written some great papers. It doesn't follow that all of their papers are great. Some of them might not bother to write up and publish their mediocre work (and some of them do), but almost all of them will still publish their merely good papers. Those merely good papers end up in merely good journals. Indeed, most great mathematicians are publishing more merely good papers than great papers.
If your paper is about the same quality as several merely good papers by great mathematicians in a given journal, then you made the right decision to publish in that journal. If your paper is better than that, perhaps as good as the merely very good papers of some great mathematicians, then maybe you should have aimed higher.
Frankly, at the level your paper is at, it doesn't matter much. If you could have made it to the top journal in mathematical physics (or some other appropriate subfield), or a decent general journal, that would make a difference, but I'm guessing you're not judging your paper as being good enough for that. People in your subfield can read your work (or at least the introduction) and judge for themselves; people not in your subfield (like myself) will see both your choices as reputable but not great journals. At a research university in the US, publications in journals like this will be thought of as contributing to your body of work, but generally not good enough to be the paper that gets you hired.
I am assuming you can generally tell the difference between great and merely good work (even if occasionally your judgement of a specific paper differs from that of everyone else). If you can't, and you also don't have a mentor, you have bigger problems than figuring out where to submit your papers.