Speed could be a bit risky depending on the distance. Arcfire does have some cast time, but it's really not that much, and it can still hit you point blank, sometimes even as you grab him. And if you block it, it's a pretty mean frame trap. If it's already ignited, Speed Shulk will have a hard time jumping over it, and I'm not sure if it's even possible to roll through it because it has a deceptively horizontal hitbox. Despite that you want to close the gap against Robin, I feel restricting yourself more horizontally is just playing his own game.
I like Jump, because it basically bypasses and counters Arcfire. Having so much vertical control renders Arcfire essentially useless, and that's one of his main tools. If he uses it while/as you jump, it's extremely easy to punish him with a fastfall attack. And Jump also gives his thunder attacks hard time, reducing it mostly to just trying to punish your landings, and since you can close the gap so fast from various angles, he won't have an easy time charging it.
Playing in the air will likely try and make them make use of those Levin aerials, though, so you have to be wary of that. But at the same time Shulk still can outrange him fairly easily in an aerial fight, so throwing out D-air when you know they're going for their U-air can tip the scales.
And of course, spacing is key. Robin has no real ways to punish ranged attacks like N-air and F-air, as all his fast options are pretty bad on range, except for maybe the first two stages of his thunder attacks which aren't all that harmful.