Some towers you don't want just set on the standard targeting modes (first, last, weak, strong, closest or random)
One example is that to get the best utility out of Snipers you want them to target the strongest enemy they can one shot kill

Other towers have problems related to the way they target
Tesla tower there's no control over the chain reaction and Laser towers fire once and are locked there for a little while

So I suggest some speciality targeting modes unlocked through research:
Basic: N/A
Sniper: target strongest 1 hit KO if possible then standard priorities
Cannon: highest density
Freezing: snowball and thing of alternative Lvl 10 ability
Anti-Air: target other towers if no enemies and power them up
Splash: targeting spins 2x speed on when aiming at no enemies and then rapid fires any saves shots at 0.5x rotation speed until out of saved ammo (up to some limit)
Blast: if there's only one enemy in range it skips a shot for a guaranteed stun/knockback
Multishot: highest density
Mini-Gun: healers and armours first if possible
Venom: poison most susceptible first
Tesla: chain by length rather than number of enemies, ricochet follows Tower priorities ignoring hit enemies
Missile: if there are no targets lauch missiles to circle the tower until the tower finds a target first missile takes 1 reload time, second takes 2 and so on
Flame Thrower: highest Density
Laser: Laser grid, rather than targeting enemies Laser Towers target each other leaving predictable laser beams criss crossing the track.

It would then be up to players to decide which of these abilities to research and use and which to turn off because they are useless for their style. Not all would necessarily work together and its an all or none targeting change not per Tower which would be particularly irritating for some towers/maps so working with them allows for a lot of different strategies