Reading through this thread I can understand that someone new at this doesn't get it anymore. So many conflicting opinions/statements, plus the fact that new participants most likely don't have a clue who are the coders among them and therefore authoritative. For newbies this is utterly confusing, despite what I assume, everyone's best efforts.
For what it's worth to OP: I always install a swap file, better safe than sorry. That way I'm sure that if my router runs out of internal memory, it has the swap as backup file to use it as 'external' memory. Most USB sticks nowadays have plenty of space, so what's 2Gb on a 4GB-64GB or even larger drive to prevent possible future problems. As mentioned before, if a script requires a swap file (like SkyNet) it will prompt you for it during install. As for your question whether to use a drive or a stick: in general USB sticks have a tendency to wear out faster, so make sure you've got a spare. Connecting a (cheap but decent) SSD drive will probably save you some money in to long run as, in my experience, they last longer then (most) USB sticks.