HDS is the way to go. I'd go with the 8 or 10 if you want to utilize all the features including structure scan. If you just want the sonar, go with the 7. I just used my HDS 8 for the first time this past week and the difference between that and an LMS is night and day, even in just using the sonar. I was able to see fish just off the bottom in 55 ft of water unzoomed. Incredible clarity. I would also suggest the structure scan and using the down scan overlay on the sonar. If you even think you want structure scan down the road, go with at least the 8. The difference is, you can split the screen four ways with the 8 and 10 and only two ways with the 7 on down.