Ditto here, I don't trust the liquids, I carry a tire plug kit in both vehicles.
I have used Slime once and didn't have any problems, tire lasted quite a while, actually till the tread wore down.

The thing is, if you only carry Slime or Fix-A-Flat and the hole is to big your screwed, so my suggestion is if you want to carry one of the liquids you should also carry a tire plug kit also just in case.