Nail clippers. Ordinary drugstore nail clippers. I used electronics dikes for years, and thought they were the bees knees, but nope: turns out nail clippers are actually way better. The cut much, much cleaner*, and with less force, and they keep their edges better. Only downside is they can be hard to maneuver with wee parts that are molded really close to the sprue, but that can usually dealt with by cutting the sprue section first.
I'm probably speaking to deaf ears here, as people do love their specialty tools (especially ones they've already paid for), but seriously: before you go and drop any money, go to the medicine cabinet and "borrow" the nail clippers to try. You will be surprised.
If you decide to buy an extra pair specifically for modelling, look for "oblique nail clippers"**. Those have shorter blades that are positioned at a 45 degree angle, so they're more maneuverable than the standard ones. A pair of those for sprues, and a pair of toenail size clippers for metal bases or other heavy cutting, and you're set.
*Some of you who use electronics dikes will be thinking "Mine cut plenty clean: I got the good ones". No: you only think they cut clean. I was super skeptical before I tried them too, and begrudgingly surprised when I did. It seems so ghetto to use nail clippers, but I kid you not, they do just flat out cut better.
**My local games shop sells these repackaged by some GunPla company or another as sprue clippers, so the secret is getting out, it seems.