I know technically there are times to use each, but I really find myself 90% of the time swinging with Normal. Depending on a game situation (really need to move a runner over, down in the count) I will switch to Contact swing. When it comes to HR's/gap shots I feel like my success rate with a Normal swing is fairly decent. If I have a count in my favor RISP with less than two outs and a solid lead (as in I don't expressly need these runs) I'll go with a Power swing.
It's interesting as if I look at my tendencies (
http://theshownation.com/players/Dezi_36/tendencies) it shows me with a Power Swing of 60 and Contact Swing of 21...so my Normal is only 19? That's definitely not accurate.