The 4200/5200 were decent units, but they're running on 2006 chipsets and processors, not a very fast redraw, and I'm not crazy about Garmin equipment since they stopped making the 2000/3000 series which were user friendly, solid units. The displays don't have a high failure rate, but the GSD22 sonar module is awful, and I can't even count how many GMR radars we've had to remove, send to Kansas, and install remans as Garmin doesn't allow technicans to either repair their domes or even open them up to fix a belt that's slipped. The 6200/7200 series are faster, but more expensive and have the same menu driven interface that I find to be clunky when it comes to marking points or even creating a route.
If you do a lot of wreck fishing, I would take a closer look at the Lowrance HDSGen2 Touch or Simrad options with StructureScan and Broadband Sounder, however it is limited to about 250' of depth to be effective, forget what the marketing says. The Lowrance HDS Touch was just announced and the 7'' model shipped out, I got my demo and was actually very impressed with the new menu interface along with dedicated home and zoom buttons, as well as the trackback feature for looking at sonar history. The NSS you need to add the LSS-1 StructureScan module, as it is not included like the new touch, and you will need two transducers. but if you're fishing deep then you'll have to rely on the standard built in Broadband Sounder (Lowrance) or BSM1 for the Simrad 12'' unit. Alot of offshore clients, and the Canyon Runner charter run the Simrad sounder gear and have been very happy with it, and the price points are a bit lower than the Garmin. The Lowrance/Simrad units can use the Navionics Platinum Plus charts, which are MUCH better than the G2 charts that come along built in to the Garmin units.
If price wasn't an issue, I still feel the Furuno MFD12 or TZTouch models are the best machines out there especially when you factor in their DFF1/3 sounder modules and DRS radars, but these setups typically run about 10 to 20% more than the NSS/5212/HDS2Touch models when you add it all up. Feel free to PM me any questions or post them right here, I've installed them all and every unit is different and people all have different opinions, so it all comes down to what your main objective is, and rank in order the importance of chart quality, sounder quality, radar quality, operational ease, support if there's a problem, and bells/whistles. It all depends on the application. Good luck in the search, this is the fun part.