On the subject of the DIA, it may be more liquid than the YM, BUT don`t forget about the leverage. You need 500 "shares" of the DIA to get the same leverage as 1 YM contract. If you look at the volumes, they are 100x the YM, but the YM`s leverage is 100x the DIA! So is it really more liquid?
Also I would imagine it, the SPY`s and the QQQ`s are all subject to the rules on PDT, so if you want to day trade them without $25,000 you can forget it.
Also I would imagine it, the SPY`s and the QQQ`s are all subject to the rules on PDT, so if you want to day trade them without $25,000 you can forget it.