Any tips on jazz guitar trios or quartets?

Another vote for Jim Hall. Also Joe Pass.

If "laid back" is one of the key qualities you want, then I should have mentioned (don't know how he slipped my mind, since he is one of my two favorites jazz guitarists) is Jim Hall. Hall's work is deceptively complex, but his sound and style is always "easy on the ears". One of Hall's best recordings, although one of his more challenging, is the duet album that he did with Bill Evans titled "Undercurrent". It's been a personal favorite since I first heard it in the mid 1960's.

All the artists mentioned have laid back stuff and stuff that definitely isn't, so any previewing you can do would be worth your while.

Would second Bill Frisell and John Scofield. Also various ECM artists like John Ambercrombie though they may be a bit avantegarde for a romantic setting.

Would add Charlie Hunter as a fusion guitarist to check out, though not particularly mellow.

You may like the Medeski, Martin and Wood sound mentioned above, but none of them play guitar. It's organ, bass and drums. They do have some nice stuff with guitartists. John Scofield comes to mind.

In an older style, check out any of organists Jimmy Smith's releases of the last 4 decades or so. Generally organ, bass and guitar. Hasn't changed much over the years, but he invented the style and does it great.

Three chanps on fusion to your taste are
Medeski, Martin and Wood!

Sd Cambell,to be more specific, I'm after the more laid back sad or romantic jazz or fusion guitar or fender rhodes. Thanks again

and don't forget about Cream.

And Jim Hall, Mike Stern, and John Scofield.

To the above, I would add Gene Bertoncini, Ralph Towner, Russell Malone, Stanley Jordan and Mark Whitfield.

Well, almost all good jazz guitarists have their own "sound" to a great degree, so it's a little hard to recommend someone who necessarily sounds like Metheny or Benson. That said, however, you should check out the following electric jazz guitar greats, whose "sound" should probably appeal to you:
1. Tal Farlow
2. Barney Kessel
3. Kenny Burrell
4. Wes Montgomery
5. Grant Green
6. Pat Martino
7. Bill Frisell
8. Larry Corell
9. Herb Ellis
10. John Abercrombie