It ultimately depends on how you want to present yourself. The short answer is: You can tailor your resume for the job you're applying for. If you're applying for an ASM position, you'll want to have more ASM credits on your resume, but if you're applying for an SM job you should show more SM credits. If you have enough SM credits to have a full resume on their own, then by all means do that. But if you are worried that your credits will look sparse because you can't fill a whole page with just SM credits, then I'd say continue to keep both on there, but maybe adjust here and there depending on the job you're applying for.
For me personally: I've done a fair amount of ASM work, mostly at one particular theatre which is pretty well-known in town, and people who see those jobs on my resume are probably familiar with at least one of the shows I ASM'ed there, if not just generally familiar with the company and the people who work there. I have about the same number of SM credits, but it's at a random assortment of theatres that are less impressive. So I'm still at a spot in my career where I think it's important to keep my ASM work on my primary stage management resume, because I have definitely gotten hired based on those credits. The same can't be said for my SM credits.
