The Mario and Luigi RPG series is one of my favorite series of the last decade, I loved all of them, but some better than others, I'd Rate them like this:

1.Superstar Saga

2.Bowser's Inside Story

3.Dream Team

4.Partners in Time

How would you say they stack up to eachother?

Partners in Time just arrived in the mail a few days ago but I haven't started it yet...
I still don't have Bowser's Inside Story...
Superstar Saga is great so far...
Dream Team, while not as good, is a lot of fun...
Dream Team is way better than Sticker Star too...

1) Bowser's Inside Story (Cause I was curious as to how his insides work ever since I was an innocent little boy and this answered my question very well)
2) Superstar Saga
3) Dream Team
4) Partners in time

Yeah I wasn't a fan of how they took out most of the RPG elements from Sticker Star, and this is coming from someone who has Super Paper Mario as his favorite in the series.

Super Star Saga.
the only one that even competes and its in a distant second is Dream Team

Superstar Saga
Bowser's Inside Story
Partner's in Time
Dream Team

Bowser's Inside Story>>>Superstar Saga>>>>>Dream Team>>>>>>>>>>>>>>>>>>>>Partners in Time

I only played Superstar Saga and Dream Team Bros. and Superstar Saga is better. DTB is still good.

My favourite Mario RPG is Paper Mario: The Thousand-Year Door on GCN.

Super Star Saga is the only one I've actually played so far, so it gets my vote. I did enjoy it though, so I'm looking forward to continuing the series at some point; I just couldn't get into it the way I did the Paper Mario games though...

I really regret waiting so long to try the Mario and Luigi games...
Dream Team is the first I played...
I knew within ten minutes of starting it that I would end up liking it more than Sticker Star (which, for the record, I did like)...
I still haven't finished it, but it's very charming, though some of the dream world sequences have been a little tedious and repetitive...