Is it sufficient to rest joists on joist hangers or should you always toenail (drive screws/nails at an angle through the joist). And does the toenail have to drive into the ledger or just hold the joist on the joist hanger?
You should always nail your joists to the joist hangers, using the type and quantity of nails recommended by the hanger manufacturer for the type of hangers you're using. Double-shear hangers, the most common type, will have special nail holes designed to direct the joist nails at an angle through the joist and into the ledger or header. Typically you'll use 16d or 10d standard-length nails for the joists, and short 1-1/2" 10d nail for fastening the hanger to the ledger or header. Here's an image from Simpson's website of a properly installed double-shear joist hanger:
Always toenail . . . just resting it on the joist hanger means it could slip out. Some joist hangers have a place for you to nail though the hanger, into the joist, and then finally into the ledger.
I would always use at least one toenail to prevent the joist from shifting around on you (either while you are working or later due to warping) It's better to run the toenail into the ledger, but just attaching it to the joist hanger is fine too. Face nailing through the ledger into the joist works fine as well.