Torn On Marketplace Analytics Tools - Need Guidance

Hey everyone. I'm torn on which analytics tool to purchase for tracking user data on my marketplace. We have mobile apps (iOS and Android) and a website, all of which have the same marketplace functionality.

I'm looking into SEM Rush (seems like it's only for website analytics), Amplitude (seems like it's only for mobile), and Mixpanel (for both?).

What analytic tools did you use out of the gate when your traffic was still low-ish? Our initial hypothesis was that the majority of our marketplace usage would be on mobile apps, not our website, but it's pretty even so far.

Maybe more of a strategic question, for marketplace gurus: Should I just be optimizing for SEO on my website (and get SEM Rush) and worry about mobile downloads later?

Open to any and all suggestions. I just can't pay for two things right now or give enough brain power to track in two places.