Well "cage" is even a pretty broad term. There are allot of types of enclosures that could be called cages. Avoid unfinished/unsealed wood. Warm porous wood if a fabulous place for bacteria to grow, and next to impossible to sanitize properly without leaving fumes for your animal. And its even easier to grow bacteria if there is humidity.
Tanks can be fine, if managed properly. The #1 problem with tanks is they normally have a screen lid, and have a very hard time holding humidity. You can cut Plexiglas to cover part, and other things like that, but it really is a pain in the a$$ if it is a humidity needing species. They also have a harder time holding a consistent heat. Which, in a larger tank, can be advantageous to a species that needs a larger difference in their temperature gradient, (like a bearded dragon.)
That said, they are ideal in my opinion for arid/desert type reptiles, diurnal lizards in particular, bearded dragons, uromastyx. etc... The only thing I will keep in a 75 gal or larger tank is that type. By the time anything else needs a 4' enclosure, it is not going in a tank. Reptile enclosures should really be thoroughly cleaned and rinsed out occasionally, and a HDPE plastic type cage that is 48' x 18' x 24' (roughly the size of a 75 gal, a little taller,) is much easier to move and clean out than a 4' fish tank.
Cages nowadays are fairly inexpensive, fairly lightweight, strong, and easy to clean. They hold heat and humidity better, so with the right equipment, it is much easier to get a consistent environment.
So there are advantages and disadvantages to both methods. I know I say this all the time, but it really depends on the species.
