Would you write "The worst tennis player around here is I" or "The worst tennis player around here is me"? The first is good grammar, the second is good judgment.
--from Strunk and White's The Elements of Style.
I wouldn't write either. Both suck, both sound pretentious and both cause the reader to stumble and break stride.
When you're going over a first draft of something you've written and you find yourself staring at a sentence like this, please have mercy on your readers. Break out your red pen, annihilate the offending text, and start over. Just a few seconds' thought will bring you to an obvious substitution:
I'm the worst tennis player around here.
Or better still, the even tighter I'm the worst tennis player here.
Match your language to your audience and medium.