Let's first determine which technology is going to best suit your preferred fishing style...

*2d will show a "cartoon like" image of stuff under the boat....
*DI will show a "picture like" image of stuff under the boat and out to the sides a few feet...
*SI will show a "picture like" image of stuff under the boat, out to the sides 100+ feet...and which side of the boat...

2d is good for vertical fishing....
DI is good for understanding what the 2d is showing...
SI is good for finding new structure out to the sides of the boat...

Rickie