Different compamies have different strengths. I always hesitate to answer these kind of questions because only you know exactly how you fish. I would suggest this narrow your choices according to price. Then :
Read as much as you can on the choices you have made. Then rate by what you have read
1. Performance - ( as in bang for the buck )
2. Reputation - do the units have good track records with their users
3. Customer service- read as many forums on each choice that you have made
4. Manufacturers web site- use for explanation of features. Do not use for purchasing info each manufacturer will cite they are the best.
5. Make your own list and rate by whats most important to you.
Example - Customer service is what matters to me the most. To Me if my unit is broke and I cannot get it fixed in a reasonable amount of time it is a expensive paperweight.
You will have to choose what is important to you. Only you know what will truly satisfy you. A lot of people do not like to read but reading will be your best friend in this endeavor. To me the research is almost as fun as the actual purchase. Try to ensure what you are reading is recent news. the newer the info the better.
Garminarmin gpsmap 1040 xs networked with Garmin gpsmap 1242 xsv , Panoptix PS 30 and PS 31. Livescope LVS 32
Ice rig Echomap Ultra 106SV with LVS 12 and GT10-IF