Rumor and K.I.S.S.
Since I only have Dynon I can only speak to that. I like it and support is good. However reading, BMA seems to generate more complaints than most EFIS? This could be old news, long fixed early bugs? I do know early BMA production and wait times generated lots of unhappy campers. Again that me be a thing of the past. BMA does have nice "FORM, FIT, FUNTION" from their ads.
Personally I want a good solid basic EFIS, reliable attitude (Dynon is GPS independent), good flight data (Altitude, Airspeed, VSI, Heading, Rate of Turn).....and good support. All the other bells and whistles are nice but not critical. Superimposing NAV or Map data is nice, but personally I like keeping my GPS nav map display separate and the EFIS doing flight instrument duties only. I think it makes it more reliable and of course cheaper.
GRT is a well respect brand and company. I have their engine monitor gear. GRT I think is best in integration of functions, in that it will accept standard data bus with "real" avionics. I don't have one but have not heard anything bad about the GRT EFIS. Dealing with them for 8 years or more with my engine monitor I find they listen to their customers and make improvements. If I go for a step-up from the Dynon, I would put the GRT at the top of the list.
The folks that design and sell all these EFIS for a few grand to $10K are all to be applauded, very clever folks. Look at the price of "real" EFIS, 10 to 30 times the cost. What's a Garmin 1000 go for now today? The Garmin is better no doubt, but what do they cost? $80k? That is more than my whole plane. Will it make it more fun to fly? Don't get enamored with flashing lights. Are you really going to fly IFR? Day VFR is your prime mission? You can always retro fit/upgrade the panel.
To me, my recreational fun flying is about doing Acro, going into remote strips, formation, travel and practicing pilot skills. I don't really need to stare at a fancy panel in my personal plane. I like looking out the canopy too much. I have lots if IFR time in single engine planes to last me a lifetime. I really don't have the desire to do single pilot IFR, just because I don't need to. If I decide I want IFR capability I will supplement the Dynon with a backup attitude instrument. May be go old school and put a Vac sucker on and an old fashion Vac ATT gyro. Its totally independent for the electrical system, right.
Frankly the older I get the more appealing a J3 is to me, which I have some time in. There is something about flying with out all the electronics that appeals to me. However EFIS is a wounderful thing for our experimental planes. It was only found in airliners 20 years ago. It was less than 8 years ago that BMA and Dynon came out?
The early EFIS in the B757/B767 I fly is pretty basic compared to some of the most fancy new commercial EFIS and "experimental" EFIS on the market. The Honeywell in the Boeing is built like a brick, all business. How much digital display do you need. They did studies of pilots and displays. After so much information, it becomes a burden to the pilot, info overload. Simple displays showing the important stuff that is critical works. A lot of the ergonomics and "human factor" design knowledge has been learned at great cost. Much of that knowlege of displays is incorporated into the experimental EFIS, basically because they copy the displays of commercial EFIS. Than it comes to preference. Try and view different displays in planes if possible. Some are sharper or brighter. Size? I went from a Boeing B737-300 to a -700 with larger screens. Ho humm. I have good eyes and could see both equally well. The larger screens where nice for compacting and combining info, but again the data overload. I turned all the display switches off I did not need and left just what I needed on.
I like the Dynon because it does the job, reliable, low cost and they have good customer service.
Last comment, integration with all Flight, Nav and Autopilot functions in one box seems desirable but redundancy is lower. Having separate FLT INST, NAV and AUTOPILOT has advantage. Of course all these things are electric. So your electrical system takes on new importance if you rely on your EFIS to stay level in IMC/IFR conditions.