3-2-1 question

It depends on the overall flavor profile you're looking for, though adding liquids to the foil won't do a lot for flavor of the meat, unless you later degrease it and use it as a base for a finishing sauce. You will have some meat drippings to add to the flavor of the finishing sauce with this method. If you could catch all the drippings during the smoke, degrease and use for a sauce-base is the best way to go.

For pork, I've used OJ for the slight tang of citrus with a milder flavor, lemon juice for the same, but the lemon flavor is stronger, yet seems to go well with almost anything. Apple is a very good match for pork, especially ribs. BTW, if you haven't tried powdered apples (ground, from dried) in your pork dry rubs, you should. I have a Cherry/Balsamic wet rub for pork ribs that's great as well.

For beef, lemon juice, worsty sauce, red wine, rum or other distilled spirits, or balsamic vinegar can add more enhancement and depth for the flavor of your sauce-base.

Most often than not, if I foil or pan/tent, I add nothing at all for liquids, going more for the natural flavors of the meat and smoke, enhanced only by dry rub. The natural moisture in the meat will slowly escape and steam the meat when foiled, and there's always plenty to do the job when I want a really tender rib.

As of late, I don't foil much anymore...straight open grates, using a wet to dry smoke chamber humidity for a good balance of smoke reaction, bark and retained interior moisture. Tenderness can be varied with cooking temp and times, looking for pull-back and using the bend-test as the main indicators for the desired amount of tenderness.

Butter is something I haven't tried, though I can imagine the richness it would add would be great with leaner cuts and lean trimmed ribs.

Eric

I have never tried butter. My rib rub is a mixture of cherry powder, honey powder, and peach powder. Seems for me the rubs add the most flavor. I double foil with apple juice. Foiling makes very tender fall apart ribs which we prefer. Some folks prefer firmer ribs. You can cut a slab in half and try them two different ways at the same time.

I use a brown sugar and paprika based rub. I let mine soak overnight in apple cider and the juice of a couple of lemons without the rub on them. After they soak i will dry them and then rub them and then let them rest for a couple of hours. Once i put them on i use the slaughterhouse spritz every hour. When it comes time to foil i spray a liberal amount on them. After they come out they are almost falling apart. Anyhow good luck with it.

If I wrap mine I will only put the mop sauce I use.

1 beer
1/4c Rub
1/2c. Apple cider vinager
1/2c. Apple juice


I like my ribs, but want to improve them.

When I wrap them in foil i put in a little sweet tea.  Im sure just about any liquid would work but it makes me smile on the inside,  , plus it feels just a bit more southern.  Best of luck.