what would be more economical

I would think it would be more economical to heat the tank. I keep my living room pretty warm but still have to keep a heater in the tank to maintain 76 degree temps in the tank.

Heater in tank is much cheaper.

i ahve 3 tanks in my room a 45 a 55 and a 10 and the normal temp without the tanks was 70 now its 78 in here no change in thermostat

Unless you had a very large fish room,heat the tank,not the room.

heat the tank, but put a well fitting lid on it.

My bedroom is so hot and humid just because of my 30 gallon tropical tank, which is at a stable 80 degrees because of the Angelfish (they like it steamy ). So if you heat the tank, it'll heat the room, if you heat the room, it'll heat the tank. But in the perspective of cost, heating the tank would be way less expensive, if you plan on getting more tanks, possibly 3 or 4, heating the room rather than individual tanks would be less expensive. Sorry for the complicated post, it's my way of talking!

I would heat the tank and I would cover the sides and bottom with rigid insulation.