"A best of" is kind of vague, since Iron Maiden seem to release another Best Of album every year or so (and for the record, I own them all... *ahem*).
Most people would recommend Number of the Beast, Peace of Mind, or Powerslave. I don't really know what kind of stuff you like, though. My personal favourite of those three is Powerslave. If you're going to just get a Best Of, I'd say "Best of the Beast".
And probably more than 90% of metal bands in the world are influenced by Iron Maiden and/or Judas Priest.