Hey, after effects and sony vegas are known so well since they're a good balance between effectiveness and usability-- they can be used by anyone from noobs to pros to accomplish a massive range of results. Therefore, beginners can approach it and can be confident that they are able to actually achieve something from the start, as well as can develop with their program and not be limited by the software once they develop as an editor.
Other programs could also be said to be like this (Movie Maker and iMovie have been used to make some pretty impressive things) but in general people seem to prefer AE or SVP, and I think that's why. Don't be worried that you're using a different program- not everyone uses AE or SVP. I know that Littleshy uses a different program (HitFilm? Hitman? Not sure, can't remember.) and Nuke is a very well known and capable program. The important thing is that you learn the basics of PMVs and what makes them effective. Often this can be achieved with any software, since good PMVs don't need too many effects or fancy stuff.
Personally, I'd recommend starting with AE or SVP. They have massive support online, since most people use it, and you can find tutorials on almost anything. I know that AE in particular has massive potential in making simple pmv's to full out motion graphics PMV's (see TheAcleps
). While SVP is extremely user-friendly and is great for people starting out. In the end, it's up to you, so good luck