Tyranitar

It really depends if you want an attacker or defender, plus your preferences. I personally like the B/SE Tyranitar because I mainly attack with mine but B/C is really solid for defense. Honestly both options are good choices.

You are going to want both in the future and both are useful now. For this one get B/C since it is guaranteed with only one TM.

Tyranitar is an attacker, so you want bite on it, period! To weak on defense

Be happy with using a Quick TM for B/C.

Using a Charge TM has 50% chance of getting Fire Blast, which loses out on a lot of favorable STAB+super effective matchups.

Turn all Tyras to Bite. IT may be a better defensive fast move but who cares? Tyra's are much more valuable as attackers than as defenders especially on raids and against legendaries. You got Crunch so B/C would rip Alakazam bosses up and the best MS into Mewtwo.

Bite and Crunch is the best moveset against raid bosses like Alakazam. You will find better use for charged TM on other Pokemons as now Pokemon Go is mainly on raid bosses and not much on gym battles anymore. That's IMHO. :)