Definitely always edgeguard him, especially with bombs.
Also, if are in neutral against Arsene, you can pretty safely spam bombs and move in the opposite direction to cover his projectile. Just wastes a bit of time.
Another thing I like to do is bait out the counter/reflect with charge shot cancel and get grabs.
In terms of movement I think they both have plus and minuses against each other. I definitely got killed at 70% a couple times because Arsene is OP. Just take advantage of Joker being forced to approach you and try to get kills before Arsene is active. Once Arsene is out, if you play smart you can time out the meter with bomb stalls, bomb traps, and pea-shooter charge shots. If you hit a true setup then go for it, otherwise (like most of the cast) it is kind of pointless to go for potential trades against Arsene. The payoff is almost always negative.