The answer is almost always inside. There is more you can do, more effectively, if you are close to it.
But you can also be effective from the outside – for example, amending Committee policy letters to address the issues that concern you, or moving Requetes to get an issue debated if the responsible Committee is not moving on it.
Bear in mind that, when you’re on a Committee, you have to compromise with the other members to achieve a set of proposals you can all live with, before you bring it to the States. If, like me, you’re inclined to be more radical, then you either need to work with a team who can tolerate dissent (as I was blessed to do on all the Committees I served on) or consider if you’d be more effective pushing for progress from the outside. But bear in mind that a lot of stuff within Committee mandates never even comes to the States, so if you sit on a Committee, there are lots of small victories – things you can do to make people’s life better from day to day – that you wouldn’t even get close to if you weren’t part of that Committee.