I've been using copper solid slugs the past few seasons during shotgun season. I find they get the job done, however several deer I've shot have traveled over a 100 yards despite being hit right in the boiler room. I previously was using Lightfields and more times then none, the deer didn't make it far at all. I switched because for some reason my gun began throwing terrible patterns with them . I tried the Copper solids and they shoot a much tighter group.

What do you guys use and if some use copper solids, how are you finding they perform?

Depends on which version, stay away from these IMO.

And the Lightfield problem, your barrel probably needs a good cleaning.
I was having erratic groups recently, used a wire brush on a drill to clean the barrel, back to tight groups.
I think Lightfields build up plastic faster/heavier that traditional sabots.

My brother shoots the RCS and loves them. He found a batch that shot really tight groups and went back and bought every box they had, about 27 boxes if I remember right. He won't even try anything else till those about run out. 2-3/4" version. He didn't like the 3" ones.

I have used coppersolids for 10 years. Also have used lightfields, and federals. I have shot maybe 30-40 deer with em. I can't say I have had one go over 50 yards. I did get a poor shot on a sika doe on Monday, and we didn't find her. Now lightfields however I have. But they drop like a hammer after 70 yards.

Bottom line is, if you hit a deer with any slug from a 12ga they measure like 0.6". And penetrating completely thru an animal 0.6" anything will put them down. If you fail to find them or they travel far with any 0.6" anything, you hit them poorly. I myself love the quartering too shot.