I have used several different F/F on all my the various fishing boats I have been on or owned.
IMHO Garmin are the best, followed closely by Hummingbird. However, I get the feeling that most of the people who complain about them not functioning properly are always at high speeds. THIS IS NOT WHAT THEY ARE FOR!
Gps covers the location & speed side of things, if you are trying to search the bottom at 25knots plus for a wreck then good luck.
Fish finders work brilliantly at slow speed giving bottom definition aswell as findfing fish. I fish my the Solent all year, I locate my spot with GPS first, then check F/F to see the bottom to search the sandbanks and holes.
If used correctly at the right speed they will give many hours of service and I always come home with at least one decent Fish.