How much boost are you using ? Are intake temps at a level where you need water injection ?
What compression ratio ? Is your engine knock limited at present ?

If you're pushing the turbo to it's limits, then injection pre turbo can be a good thing. If not, then less so.

If intake temps after the IC are still very high, then injecting between the IC and Throttle can be of help.
If they are low and the injected liquid may not actually vaporise, then port injection may make the most sense. Especially as your intake manifold probably wont promote even liquid distribution to each cylinder

Although with port injection, your IAT sensor will not see the changes, so if any tuning compensations rely on seeing this change, it may be important.

AEM do a flow meter with a 0-5v output, which is the safest way to apply tuning changes when water/meth is being injected. If for any reason the system fails, this is the safety backup. No tuning adjustments will take place. Obviously you need an ecu that can make use of this though.

Aquamist have actually just released some nice nozzles with built in check valves intended for port injection usage. Saves using solenoids to control flow.

Of course it all depends on the complexity of a setup you want. Is it something simple, or fancy ?