Always on normal, did it on elite once and didn't see any difference in loot (the only difference is that I blew up once or twice).
Honestly though, just play the game. When I was working on Rom rep I'd do 7x Acamar runs for the Tau Dewa patrol daily... would consistently get ~200k of vendor trash. Run STFs and you get decent stuff to vendor trash, and every now and then I get drops from ISE that are actually worth selling on the exchange.
If you are bored and want to do something different look at mission replays. There are a few of the Cardassian front missions that award shields that are fun on the replay -- 15 minutes, something to do while you wait on a DOFF assignment to end or your STFs to cool down.