I so agree, don't base your decision on shelter cats being the way you have seen them, they are afraid, in cages, lost or abandoned and confused, and so sad. Cats take time to really show their true personality, and you just can't determine it in the cage. This is why I always think an older cat is easier to learn more about their personality, they are usually more calm and often times, the shelter workers know enough about them to give you an idea of what you are looking at. They want it to work out, so they are not going to talk you into taking a cat that has crazy behaviour issues if you are looking to avoid that, they want the best outcome for the cat too.
I have a cat that my vet is fairly certain is a main coon, probably just a mix, but has the look and characteristics of one, and he is the sweetest cat I've ever owned. He is my avatar picture. They are pretty quiet, laid back cats, he is pretty shy with people he does not know, he has this very distinct little meow that is common in maine coons. He is such a sweetheart. All 3 of mine are strays, they all found me and I can't imagine my life without any of them. My biggest snuggler and lap cat is Stephano, a solid black little boy that we found int he woods behind my work a year ago. We believe he was dumped, along with his brother, and we were lucky enough to find a home for brother and I took him. Most lovable cat I have ever had, he appreciates his home so much, he was just so relieved when we saved him, he literally did not leave my lap or my arms for the first 3 days he was so exhausted and relieved to be loved.
I always believe the cat chooses the person. That's the way it has always been for me, always, every cat I have ever had. I would go around to places that have rescue cats on the weekend, like the Petsmarts and Petcos around me have rescue groups that bring their animals there on the weekends to try to find them homes, and start holding some of them and checking them out. Every one I know that is always on the lookout for a cat, they seem to find their cat this way, they may hold 100 different cats, and it just takes that one to know that it is a fit, you just feel it. They just relax in your arms, and lick your face and melt, and then they melt your heart, and it's done! You've been picked!