Until you get up to the liquid metal category, all the good ones are within 1-3C of each other. AS5 shows its age in two key ways: it has a burn-in time of up to 200 hours before it's fully effective, and it's ever so slightly capacitive if you spill some and it bridges current. It's still perfectly good, though, and if it's what you can get your hands on easily you're not missing anything.
I just picked up a tube of MX-4 because it's good, it's cheap, it takes years to even start to look like thermal cement, and you can literally paint your motherboard with it without having to worry about shorting anything out. Just avoid the cheap Chinese crap that comes in jars, bottles or syringes the size of a hot dog and costs $2.50 for six metric tonnes of paste and you're good.
Funny story about those: they are highly conductive and will fuck your shit up.
Looks like I will be going with MX-4 Thermal Paste! Thanks all who gave their input! Cheers and a happy new year!