Depends on
1. If you're gigging with it
2. If you're gigging with it and want the cranked SLO tone, which is a separate and special thing
3. If money is an issue
They both sound great, with the 100 being a tiny bit more "special" sounding because of the bigger low end and push. The 30 is absolutely rad though.
If you've generally got really good sound reinforcement at your gigs, and money is an issue, the SLO30 is probably good. You'll likely be able to get closer to the sweet spot at most gigs.
If money isn't an issue, get the 100 and a nice attenuator, full stop. Then find exactly where the sweet spot is for the tone you want and control your level with the attenuator - set and forget.
If you're playing dive bars and small clubs, get the 100, whether you can afford an attenuator on top or not. At least in my experience, even a lunchbox as big sounding as the 30 is going to be fighting in some situations if you've got a drummer that doesn't hit like a bitch.