Gary, obviously.
Comparing a "ladies' man" with a guy who's rude to everyone regarding who's nicer is like asking "Who's the most powerful pokémon; Charmader or Arceus?".
Paul couldn't care less about Dawn while Gary - once seeing that Dawn was a fan of poetry and his grandfather - made up a short poem for her.
It took Gary only one episode to be nicer to Dawn than Paul has been throughout the entire journey in Sinnoh.
No offense to Paul though. He's one of my favorite Pokémon characters. But seriously, only an Ikarishipper who's blinded by headcanons would vote for Paul in this case. He doesn't care about her at all.

^lol agree

Paul didn't care about her at all, he was a jerk to her. He couldn't even remember her name for the longest time! Gary could sometimes have given her an attitude, but was nice to her overall.

Gary would definitely treat Dawn better than Paul would ever do.

I like Paul but he is never nice with Dawn.
On the other side Gary really cares and respect her.
He is really nice to Dawn and Dawn seems to be comfortable with
him.
But I think Gary is not comfortable with Dawn.