I think it's too very different kinds of knowledge. Tony Stark's an engineering genius, but they've also hinted he's a bit clueless when it comes to other things. There's a great little bit in the first Iron Man
when it's pointed out that Tony doesn't even know his own social security number (I just did a Marvel marathon last week and watched all the films in order
The Riddler is brilliant, but it all seems very focused through the lens of puzzles/ riddles/ challenges. If he was a real person, there'd probably be some autism-spectrum diagnosis you could make. His knowledge base seems much wider, but he's limited by how he can use it.
I'd guess the Riddler would kick ass on Jeopardy
, but Tony would be the much more entertaining contestant.