When MSFS was launched, I tried various aircrafts, just to see which I would like most. Given that I’ve always loved turboprops, it’s not a surprise my attention was drawn to the TBM 930. It was fast, it could land on shorter runways, so it became my choice for my around the world flight.
While I’ve flown other aircrafts since then, I always tend to return to the TBM 930, something with it that really speaks to me 
You can have a lot of fun with the Shock Ultra (which included being blown backwards down the runway at Colerne EGUO before the wind effects were “adjusted”).
I also have a soft spot for the Pipistrel Virus, which I flew a lot before the third party GA types started being released.
Both of those are among my favorites.
The Shock Ultra is just ridiculous. Part overpowered Piper Cub, and part paper airplane. So much fun to be had in that one.
And the Pipistrel has air brakes! Very slow plane that can be flown in exacting ways.
I had a spell of landing the Ultra in extinct volcanoes and then seeing if I could get out again - it often ended badly!
I often try to land it on helicopter pads. Many hilarious results. But the successes make it worth it.
I’ve taken off in the Shock without realizing it. You could probably launch from GA parking.
It is often right next to a helipad so I have taken off from parking many times!
I love the Mustang from the basic reno pack. I found it a challenge to master and keeps me on my toes.
Given the oil rig packs now on Flightsim.to those shoudl be the next Ultra challenge!
For me it was only the A320neo and the 787 since I only insterested in big airliners, and not so much on GA.
I flew the 787 more often at the start, until I realised the difference of philosophy between Airbus and Boeing, and I end up ditching the 787 entirely and just fly the A320neo exclusively.
That is until I installed FBW A32NX, which improved the default A320no so much, I ended up ditching the default A320neo entirely.
So now, to answer your question, there’s no best default aircraft from my perspective. Because I uninstalled every single aircraft that I can uninstall, and leave just the default A320neo for air-traffic purposes, but I stopped flying it entirely.
Really need to give that and the T6 some more time. They are excellent.
I feel for you tube liner flyers.
It is kinda like you already beat the game before MSFS came out… all the vanilla content is too easy and you have already played it.
So you must wait for third parties but of course, the most complex aircraft take the longest to build. So joke’s on you! You have to keep waiting.
That must suck and I am glad you have found a few planes to appease you along the way.
I am having an absolute blast learning my way through GA types and systems so MSFS is full of planes for my skill level. Same with 3rd party add ons. I’m finally getting into some multi prop planes and getting a new quadrant to handle some added complexity.
I promise you will have more planes soon. I am sure you already have your eye on a few.
To be honest… If you put me on a GA plane and manually flying… I probably don’t know where to start… to me GA planes are more complicated because there’s a lot of skills involved. From my perspective GA flyers are more skilled.
For tube liners, all I do is press a few buttons and off I go.
Here are my top three and a sentence.
A320
C208
TBM930
Have you tried a Cessna Citation? They handle like a jet fighter with an impressive Vx. The TBM 930 would also be a good transition.
You could work your way down to a taildragger. 
The 152. Hands down. To be blunt, it’s the biggest airplane they’re capable of simulating with any level of accuracy. I can’t believe they didn’t partner with Garmin and use their pre-existing avionics simulation software. Either stick with round dial aircraft or put some effort into at least getting a Garmin 796 right.
Cessna 152 by far.
The Cessna 172 with Steam Guages would have to be my favorite. Interestingly, during the Q & A held a few days ago, it was said that the C-172 would be the next aircraft to receive the new propeller settings (SU-9). Hopefully that will include the steam gauge as well as the glass one.
Since the last T6 update. I think it’s a great plane now ( except for the ridiculous icing effect).
I was never much of a commercial airline type so I tend to not fly them. But the citation and longitude is right up my alley as an executive jet because of the handling.