This is a fun question. Processors that have hyperthreading duplicate the parts of the CPU needed to maintain state, but they don't duplicate the parts that run the actual logic. So if you compare a single core hyperthreaded processor with a dual core processor without hyperthreading the dual core one will be faster.
However it gets a bit more complicated than that. Oftentimes processors sit idle while waiting for the rest of the system to catch up- for instance it may have to wait for memory to get loaded from RAM. Processors with hyperthreading see a boost in performance here because they can run the second thread while waiting for the operations needed to run the first thread- thus making these processors about 30% more efficient.
So while more cores are definitly better, if you are comparing two processors with the same number of cores and all else is equal the ones with hyperthreading will perform better.
One thing to note is that AWS provides vCPUs in pairs, so even though they are giving you the number of threads you can always be sure you're getting individual cores along with them.