Comparing these two is like Ford vs GM.. One thing I've heard is that customer service from Humminbird far out does that of Lowrance.. As for the HDS7, you can get a 858c HD for $50 less at BassPro..
I've also read about the menu system on the Humminbird being quite a bit easier to use. I'll be in the market for a updated sonar this year (Currently have a 788ci), I'm thinking 898 HD SI or a 958, can't make my mind up!