Chirp, chirp, and more chirp...

Regardless of what brand you are looking at, you WANT to get CHIRP. It doesn't matter whether you are on DI, 2D, or basic sonar.

A normal sonar with a 83mhz/200mhz transducer will only send one signal down to the bottom at a time. IE, either 83, or 200 depending on your settings.

CHIRP sends multiple signals in different frequency ranges. A standard sonar will pickup baitfish as a ball whereas chirp will actually pick up individual baitfish. This is the difference between sending one frequency range pinging the bottom and miltiple diffrent signal ranges at the same time.

Here is a link to the best description of CHIRP that I have found:
All You Wanted to Know about CHIRP Sonar - Wired2fish - Scout