I've played so many games against a decent GL, and so far it seems fairly even. Harley can poke from long range with guns. I think the start-up time on the gunshots is faster than GL's projectiles, so you can pre-emptively hit him out of it if you know he's going to try and harass you with green darts. At mid-range you can't be too careless with jumps, he can grab you out of pretty much anything. He's probably the most dangerous at that range and that's where he'll want you. I usually use SS to close the gap where I can try to harass him up close with a few strings, and hopefully get a chance to mix him up.
This is just my week 1 impressions. One thing i've found is that Harley is not very meter reliant in general (EX cupcake bombs are really good for keeping away though), which is good since she can save it for other things.