I can't speak for anyone else, but I did a recent analyses of my trading and found that I tend to lose money more often when I trade between 500 and 300 share lots. I'm sure it's more psychological than anything, but the choppiness of the market tends to shake me out more than usual, and I've tried to compensate for that by setting my stops a little wider. What I have found is that 200 share lots tend to be the optimum amount for me. I just find it easier to take a stop loss with that position. I've also tried trading 100 share lots, but I find it very difficult to make any money since decimals went in effect. With the penny spreads, if I get a .25 move, I'm doing great, and if I get a .50 move, that's a homerun. I'm not saying that everyone should do this--I'm only saying that it's working for me. Regardless of your trading style, I think the recent market conditions has caused most traders to have to re-think their systems; and, for me, this is just my way of adapting to what the market is giving.
In fact, one of the subscription websites uses 200 shares per trade. They are happy to hit singles and doubles to win the game vs counting on home runs. Nice idea stockerup.
I do opening orders in odd lots usually 130 shares, the fills are soo much better than in even lots. inmate451 truly irrelevant, when opportunity knocks you had better be there!(with a even lot order of course)