Soarneck brings up a good point...
All gliders are not created equal.
I have towed 40 % Foxes that are comparitivly slippery, and 40% Minimoas that are more like trying to tow up an open umbrella.

The minimoa has one speed, slow, no matter how fast you try to tow it it will just try to climb instead of going faster. The trick is to fly the tug within the the speed envelope of the sailplane. Caution must always be used with regards to the strength of a vintage type airframe. I often will drop flaps 10 degrees on a powerful tug when yanking up a smallish vintage ship, or for inexperienced pilots with smaller modern ships.

Towing a 4 meter modern ship, (what I assumed from the original post) can be done with a lot of variations.
As stated, what is best to do for efficiency is to translate speed into altitude by going up, not cutting throttle. I have towed 4 meter and smaller modern ships nearly straight up tp an altitude of 1200 plus feet in less than a minute. The tug had a 100cc Brison at the time. Sounds dangerous, but actually not. airspeed is relativly low, rate of climb is high.

Some prefer a more scale like tow in all situations, in which case you can as stated by SCATpilot, tow almost any sailplane with any tug, as long as you have the requisite skill.

When I first started towing, we simply did not have an option. We used Senior Telemasters with OS 1.08 two strokes. We towed up to 6 meter 15 plus pound ships this way.

Tow pilots just need to know that there is a throttle, and that every sailplane is a little different. Experience does the rest.

JD