1P, 1K, 6K, 4K if they haven't insisted on pushing right up in your face, ssK, mid punch hold, low hold and neutral throw are all pretty solid, in my experience online. Simply blocking isn't a bad move either, as the fast moves people often throw out to begin with are either unsafe or give such little advantage on block that it doesn't matter. You can try 66H+P, though if lag's bad it probably will be beaten.
1P is my particular favourite since on the rare times you do meet a smarter player online they'll often begin by blocking low (and dumber PPPPP-mashing players will simply be beaten by it) and 1P gives you a ridiculous time to buffer inputs, so blocked or not you can get in virtually anything else you want afterwards; 46H+P, 46P+K, hcfH+P, 64H+P and, if you're nimble and comfortable with using a shortcut, 614H+P all come out ridiculously quickly after 1P (on block or otherwise). Between that and the lag inherent in even the fastest and smoothest connections, you're pretty much guaranteed to be opening the round with a big damage throw. That's going to scare the hell out of your opponent so you're free to trick them into anything else you want and they'll be very wary opening the next round.
