I've been to both, Maldives once, and Mauritius twice (got married in Mauritius actually). I would go back to Mauritius again in a heartbeat, and although the Maldives was fantastic, I wouldn't be desperate to return (don't get me wrong, you wouldn't have to twist my arm to get me on a plane to the Maldives

)
The main difference is - in my mind - you go the Maldives and you are on that small stunning island, yes you can go a boat trip to another small stunning island. And the snorkelling in amazing. BUT, in Mauritius, you get that tropical island feel in your hotel/resort, and the snorkelling, and yes you can go on a boat trip, but there's so much more on the island to do; small towns, a city, wildlife parks, waterfalls, nature reserves etc etc.
Sorry i seem to have gone on a bit, just my opinion, hope it helps.
Oh yes, i went to Mauritius in Feb and it was hot hot hot (not unbearable) and some stormy tropical rain, also went in May, not so blisteringly hot, but not a cloud in the sky the whole time.