Lots of pros and cons for sure, for the best high frequency sonar imagry (side scanning and down scanning) for your budget, the raymarine element is a hands down winner "the 3d is fine, but the hypervision is where the party is at" 7"HV model with the works is at $1200, quad core processor, its by far the beast-iest of those smaller entry level systems. , Hummingbirds Mega imaging plus is a better system for sure but to obtain that you need to head up to the 8" unit. pushing your budget.
So thats just where the game is side imagign wise but of cause there are a lot of things at play
Mapping, Garmin has inland mapping pretty well covered with TOPO mapping if you head inland, though costal , all brands running nacionics will be pretty good. it will be tricky to find a SONAR only system now days other than in the upper end of the range wise.
By going to the echomap Plus range you do open yourself up to some cool features in the future such as Livescope from garmin, theiur LVS12 and more expensive but better LVS32. these do offer half decent everything, usability size etc for the money.
Feel free to shoot through any questions
Moose