In 2009 we did a major refit. The boat came to us with a mixture of Furuno radar, Furuno "GPS Navigator" (sort of like a plotter but without the chart background), Cetrek greyscale (ugg!) chart plotter, Lowrance fishfinder, President (non-DSC) VHF, and Standard Horozin DSC VHF.
We started with a market survey to identify decent local installers, picked the best three, and then polled those for ideas about a more capable networked system, adding autopilot and AIS, standardizing the radios, and adding some redundancy for depth sensors. At the time, I mentioned I'd prefer a networking solution from (at least mostly) a single manufacturer, and I'd like to be able to keep the radar and existing "GPS Navigator" (for redundancy) if possible. All three installers zoomed in on a Furuno suite.
At the time, Furuno's NAVNet 3D was the greatest thing since sliced bread -- especially compared to the Cetrek's glacial redraw time... and MaxSea's Time Zero seemed a useful laptop counterpart to the plotter, more redundancy.
So we ended up with an all-Furuno system except for ICOM radios. Kept the old radar, kept the "GPS Navigator" (but moved it). Added NN3D plotter on an MFD-12, Autopilot, AIS, fishfinder (not networked) and separate DST sounder. And we run TimeZero on a laptop. Changed to two ICOM radios (so each radio works the same way); Standard Horizon was the other contender, and installer recommended ICOM for that particular year, sounded OK to me.
Even today, it's still a very decent system, can't think of anything more I'd really need.
Can't overlay the old radar output onto the plotter, though. Would have needed a new compatible radar for that and I was already pushing the budget, a lot. I usually prefer a separate radar display anyway, and I didn't want to give up screen real estate (by splitting) on the MFD so that's not a big detraction. OTOH, if I were starting from scratch, I might consider overlaying radar on the plotter and saving some helm space for all the various displays. Same with the fishfinder; at the time I didn't really want to clutter up the plotter... but since then then I've about decided I could live with that in order to arrive at a slightly less cluttered helm. (We only fish during a ~25 day season per year anyway, maybe 10-15 outings, more for shakedown after winter than anything else.)
At the time, networking needed a serious mixture of NMEA0183 and NMEA2000 protocols. Now, that might have migrated more toward NMEA2000, if so, probably a slightly simpler install.
We don't have "touch" screens (I would only abide that if accompanied by hard keys/knobs/buttons anyway) and we don't have any Wifi feeds. We don't have engine displays on the plotter; could do, but with mechanical engines, it'd take new sensors and wire runs (pain in the neck), and real estate on the plotter... We didn't do the Sirius weather sensor, no loss, for me. We didn't do a camera installation, ditto no loss.
If I had it to do over again, I think I'd be very satisfied with a Furuno installation. We've had Raymarine components in in earlier boat; would have been OK with that, maybe, but the installers suggested networking all the Furuno stuff together (and given our legacy equipment) would be easier. Can't speak to Simrad, though; no experience.
I've had to read the Furuno manuals to learn how to work everything. Folks talk about how "intuitive" Garmin systems are... but I'm about as intuitive as a rock, so when I've yutzed around with boat neighbors' Garmin systems, I haven't seen any magic there. They couldn't figure something out on their system "intuitively" and I couldn't either, had to get their manual out to figure out (for them) how to do something. And complex systems usually come with complex operating regimes. IOW, I don't see the Furuno operating instructions as being a factor one way or the other. For me.
Edit: I'll add a comment about Furuno USA support too... Good! I've only had a few questions over the years, but the combination of direct support and forum have been very positive. Most recent example was about replacing the old "GPS Navigator" GP-36 DGPS unit, since the 17 year old monochrome display -- with 9871 NM under its belt -- is losing some pixels. I wondered if the GP-39 WAAS-corrected unit would be a drop-in replacement, overnight answer was yes, all good.
-Chris