Get the highest intensity that you can afford. UV effectiveness is determined by exposure time and intensity. For UV to help, you need enough throughput to turnover the tank frequently AND enough exposure time within the tube to kill EVERYTHING.
Look at the Gamma fixtures. They use T5 bulbs which gives more power per watt. They can be configured for HOB that is great to "pop on" "pop off" for occasional polishing. There is a flow chart that indicates min and max throughput for each size bulb. You want to be in the high-side of the range for protozoa for most effectiveness.
Combining UV and medication can be a great way to fight tenacious infections. But FSM is right in that you should try to narrow down the cause in order to get the best remedy in place.
UV can be great for killing waterborn parasites and will wipe out waterborn algae as well.
There's no silver bullet though.
Want a recommendation - Gamma 24w UV, with a mini-jet pump makes a single-piece unit to HOB. Have larger than 90g tank, get as close to 400gph with a 1/2 inch outflow connection as possible.
Good luck,
AB