My experience/opinion, worth what you're paying for it:
I just purchased a dual-screen 10" Dynon HDX system and a GPS-175 (they delivered last week).
One of the big factors in choosing Dynon was that I had experience with their equipment already--my dad put a Skyview in his RV-6 eight years ago and I've been flying with it on and off since then. I remember my first flight with it after he upgraded and there were two things that struck me: first, visually it really resembled the big jet avionics package I had a little experience with at work (I'm an aircraft systems engineer), and second, I found it really intuitive and easy to figure out--so much so, that I was showing him how to do things with it and I hadn't even read the manual yet.
At Oshkosh a few days later, I tried out a couple other vendors' systems, and none of them seemed as intuitive as the Skyview (especially the non-touch G3X that I couldn't make heads or tails of). I repeated the experiment in 2016 and came to the same conclusion.
As the time came close to making my decision and placing an order, I started taking a hard look at the documentation (both for installation, and use) from Garmin, Dynon, AFS, and GRT, priced out some options, and started playing with rough panel layouts for each of them. I didn't use a clean weighted-average score sheet like the one my wife used when she decided whether to marry me (seriously! she showed it to me one day), but it was more of a general qualitative evaluation. Some vendors offered some really neat features that I liked; others were lacking certain functions I really desired. Some had good documentation, others really poor. Some answered lots of my questions; others... well, didn't answer anything.
In the end, beyond familiarity and "intuitiveness", I felt that Dynon offered the best overall combination of features I wanted/needed, very good overall documentation, and good ease of installation (including the availability of a special "hub" board provided by another VAF member to make the wiring easier). Fitting things on the panel was a little more challenging with the Dynon (the autopilot and knob modules take up some space but based on experience in Dad's airplane I felt they would be really helpful with the "expert" autopilot compared to trying to drive it all via the screen). My runner-up was GRT; I liked the feature set and capabilities, and the ability to integrate with more third-party equipment, but in the end they were missing one or two things I really wanted, and the documentation was challenging to get my head around.
As far as the IFR GPS, I went with the GPS-175 in large part because it was the most affordable option, and it would fit in the space I have left on the panel (see the Dynon module comment earlier, plus I have an SDS programmer in the center stack). It's not as deep behind the panel and it's a really light unit--first time I picked it up, it felt like an empty case. That said, I'm not yet instrument rated--my plan is to work on the rating after Phase I is complete and I'm comfortable enough with the airplane. Hopefully I can manage that with GPS only, though I did leave room for an MGL N16 if needed.
Beyond the wiring hub though, I didn't really look at any pre-made options. My aircraft is different enough from standard it would have made things challenging, plus I like wiring. Some guys really get into fit-and-finish; I like to sit and make harnesses.
One thing that was neat (at least with Dynon) was that they make 3D models of their equipment available for download. I simplified them and printed out dummy units for most of the components, and was able to lay components in place and start running a lot of the harnesses and tubing for things even though I didn't have the actual units yet. In fact I'm still leaving many of them in place for now to prevent FOD and/or shop rash.
Edit: In general, wait as long as you reasonably can. Like other electronics, this stuff is getting upgraded frequently. I went ahead and pulled the trigger on my avionics order when I saw the Lycoming price increase, figuring it was only a matter of time before avionics prices went up too.
Disclaimer: I'm a low-time pilot and my airplane isn't done yet. YMMV, terms and conditions may apply, views expressed do not necessarily represent those of anyone here, no warranty express or implied, no substitutions exchanges or refunds.