Whats more reliable, what things affect rate of success etc?

Disarm
As Daevryn had mentioned, this is the worse of the lot you have listed. Factors include knowledge of weapon (eg axe, sword), disarm skill, weapon type (eg two-handed is harder to disarm, while swords are easier).

Hook
Works better than disarm. Probably strength, skill and weapon-type too.

Entrap
Works fairly often. The good thing is you can entrap while blinded. Probably entrap skill, strength, and weapon type. Can't entrap small weapons.

Strip
Strip can start a combat and you have a chance to catch the weapon based on dex and skill. Highest chance of disarm.

These are no means correct. Just my observation, experience and $0.02 worth.

>Whats more reliable, what things affect rate of success etc?

There's some weapons that can't be disarmed by some of the spec disarms, but generally the three spec disarms are all better than normal disarm for a weapon they can target.

Strip can initiate combat, and the warrior gets a chance to catch the weapon instead of it going to the ground.

Entrap has a round of pre-lag and a round of post-lag.

There's more, but that's some of it.

I assume that if one of the skills doesn't work against a particular type of weapon, that it is specified in the helpfiles? Like hook and entrap both say they cannot disarm daggers. Is that it?