Should I upgrade my GPU or get an SSD first to fix FPS drops?

I would get an SSD first, especially if the whole PC is running from the hard drive. The system and games should feel much quicker to load, and it may help with stutters when an open world is streaming in new assets.

Just don't expect it to turn low frame rates into high ones. If the GTX 1660 is struggling to render a scene, an SSD won't fix that.

For higher FPS, the GPU is the upgrade to look at. A 1660 can have a rough time in newer games, particularly if low settings are already needed for acceptable performance. An SSD is still a good buy, but its effect on in-game stuttering depends on whether the drive is actually holding things up.

Try monitoring GPU usage and frame times while playing, and note whether the worst hitches happen when entering a new area. High GPU usage with consistently low FPS points more toward the graphics card. Hitches during loading or traversal can point toward storage, though those checks aren't conclusive on their own.

For the SSD, check what your motherboard supports and compare the price of a compatible M.2 NVMe drive with a SATA SSD. Either is a big step up from a hard drive. Put the games that stutter on it, not just the operating system, so they can load their assets from the faster drive.

GPU recommendation really depends on budget and resolution. A used RTX 3060 could be an option at the lower end, while a used RTX 3080 or 4070 Ti is a bigger step up. An RX 9060 XT is another card to compare if it fits the budget.

For a used card, check its condition and the seller's return policy. Also check your power supply capacity, required power connectors and case clearance before buying.