I am just gonna go ahead and assume that you mean "potential payout" here instead of upvote, since one could have hundreds of upvotes but will still only total less than a dollar.

You can check all popular tags used in Steemit and see how much that tag's potential payout is here: https://steemit.com/tags

Taking a quick look at the link above, it seems that many people have success on blog, cryptocurrency, bitcoin and art tags.