Canada

In principle, I like the idea of having a check on Parliament. Not a block that can prevent things from happening, but something that can slow things down a bit when necessary and maybe cause Parliament to rethink what they're up to or moderate their actions. In general, I think the Senate is reasonably effective at that.

In principle, I like the idea of some kind of regional representation. Not so much that the province with small populations can stand in the way of sound national policy, but enough to limit the exploitation of those provinces in favour of the ones with larger populations. I'm not sure that the Senate has been as effective in that regard as it could have been.

I really like the idea that no Senator can be an active member of any political party. They should all sit as independents. In fact, I would argue that no Senator should ever have been sitting member of Parliament, and maybe not even held party membership for at least a decade.

Finally, I would like to experiment with sortition (random selection instead of political appointments or elections) and a properly constrained, yet not powerless Senate seems like the perfect place to try it out.