The HDS Is $28 more

http://www.hodgesmarine.com/Lowrance-Hds-7-Gen2-Insight-Usa-83-200-Khz-T-M-Tra-p/low000-10530-001.htm

http://www.hodgesmarine.com/Lowrance-Elite-7-Hdi-Gold-Combo-83-200-455-800-T-M-p/low000-11051-001.htm

I depends on what technology you want.

 

To get the scan technology for the HDS, you have to purchase another accessory (Structure Scan LSS-2).

 

The Elite-7 HDI comes with the transducer that gives you Down Scan and regular 2D sonar.

u WILL want the hds  i hear the elite 7 is very slow

I'd probably go with the HDS because you can expand on it with more options. Although the elite is a decent unit with more features right off the bat, that's about where it's going to stay. With the HDS you can expand and add way more in the way of accessories to it. That's just what I would do though, if the Elite has everything you want then no reason to go for the HDS.

One has map chips. Weigh that in too.

This is for the front of my boat & transducer on trolling motor

i would just buy an hds7 gen2 touch on ebay for the same price 

I recently purchased tow of the Lowrance Elite 7 fshfinders for my older Ranger. They were a great upgrade over the 10 year old electronics that came with the boat. The fishfidners work well, and the mapping works great. I personally thought that the DSI was going to be more crisp and clearer picture than it actually is. You may want to look into the version with CHIRP SONAR as well. Overall not a bad unit for the price point.