I look at benefit/cost ratio.

I agree, the stock skids + belly guard is #1.

Next in my book is the front guard. It's very affordable and it prevents damage to radiator/condenser. In places i offroad where you have to drive through some water/mud, you're very prone to a large stick or something popping up and getting caught in that area (i've seen it happen).

Rock rails and rear sliders are 50/50 in my book.. depends on where you wheel and if you have a factory hitch. If you don't have a factory hitch, then the rear sliders double as recovery points and they take the lead.

That's my $02 anyway