Speaking as a current Sierra owner, '79 C24R, I can say the plane flies great, solid IMC platform for IFR work, low maintenance for a retract, gives a true 130-132KIAS on 9.2gal/hr, can carry 4 full size adults. (I hate it when others dispute factual information that REAL OWNERS give when they are only speaking an opinion that is misleading.........). Only drawback I find is it takes a bit more runway for takeoff/landing margin......just plan on using Runways with min 2500'.
It's not the fastest, but may be the roomiest interior and is very comfortable and solid beech quality, meaning "fit and finish" and quality of materials and structure of wing spar/landing gear make it a very solid feeling platform. I'm very happy with mine. As another member mentioned, the 5-10Kts difference in some of these other similar powered models never amounted to much net operational difference in a 300-400 mile trip which is pretty typical of my travels.
I had a '58 J35 Bonanza, this Sierra is much easier on the pocketbook with fuel burn and maintenance and none of the V-tail worries. I had a Citabria before that. I have flown 152s, 172s, 182s, Cherokees, Archers, Cherokee 6s, DA20, DA40, Cheetah, Tigers, Bonanzas, Skippers, Sundowners, Duchess, Cirrus SR22. I would love to have a DA40/50 or Cirrus but that's a whole different financial equation that I can't do right now. I wanted to get the most VALUE for the budget that I had to play with, that's why I ended up buying the Sierra.
There are lot's of choices, no one should be so ABSOLUTE for/against a plane model because everyone's tastes are different. I was considering (actually searching to buy) a Grumman/American Tiger AA5 because of it's speed and efficiency at 180HP, but the plane felt "light in the pants" when in a little IFR turbulence and not as easy to keep on track so that changed my mind. I still think that a Tiger would be a joy to have, but for carting my family around, I felt much more "assured" with the Sierra.
Mooney's are great, just a little cramped for my taste......and my family's opinion counted much in my decision on "cabin comfort" (Wife and two daughters.) Piper's are solid just not as well appointed in my opinion, and Cessna's are "high wing" and more expensive and don't provide any advantages that I can see. The aforementioned models are typically much more expensive to acquire than the Sierra, so again, like another member mentioned, I chose to buy a more recent model (1979 Sierra vs a Mid-60's to early 70's model of the others) with better avionics and pocket the savings for more flying. Just my two cents.......