Mainly US index futures. Occasionally Kospi and Euro futures in the early and late mornings respectively..
Futures mainly cause of the leverage. Also no uptick rule, transparent liquid market, cheap exchange membership advantages, low commissions, fast fills (no waiting for specialist on NYSE/AMEX stocks), index products unlikely to be halted or as susceptible to news as a single stock could be, no PDT rule (allowing more capital to be put to work elsewhere), a wealth of ancilliary data (e.g tick, trin, breadth), no need to scan hundreds of candidates for trade opportunities and make frequent position size / stop etc. calculations (corollary: instruments' personalities are easier to learn if one studies only one or two all the time), I'm awful at mornings and wakeful at night so the hours suit.
These are actually the reasons I stuck with (index) futures. I fell into them I think quite by chance (first "trade" was spread bet on the FTSE) and could equally have started with stocks, spot forex or pork bellies.