For my money? Schwalbe Marathon Plus.

No tire is perfect (and Gatorskins are good). Sharp metal object will puncture even the most 'bulletproof' tire, but for glass, goatheads, etc., then the Marathon+ is great.

FWIW, I think tire liners causing flats is a grossly exaggerated problem, and at most, you might have to sand smooth the edges of a liner to a nice taper (I have been running tire liners in my streetbikes, mtn bikes, and now recumbent and velomobile for over 20 years, and never had a flat caused by the liner.

Since most of my riding is commuting (although I do ride a lot for fun, I don't have separate machines for that), I go with what is the most flat proof. I'd rather be a little slower, but be able to get to work without worrying about flats.

Currently: Velomobile - Marathon+ (2 x 20" front) 26" rear with Mr. Tuffy liners. The fronts also have Flat Attack sealant in them (the rear doesn't currently). My recumbent is running Schwalbe Kojaks, which are a little faster, but I also have liners in them.

I check my tires ~weekly. Last sunday, after a 30 mile ride, I checked my tires, and pulled a total of 3 mostly intact goatheads, and 8-9 broken thorns from goatheads out of my tires. No flats.