You are asking a very broad question. It would be better to ask for strengths & weaknesses in a specific model U are interested in, but here goes. We have a C 30 which would be a great boat for weekends, & a good first timer sailboat. She is very stiff & weatherly, a good performer & very forgiving under sail. She doesn't heel excessively & will tend to round up if over powered. The cabin size & accomodations are unmatched for a 30 footer. The most bang for the buck around. But potential rot problems of plywood core in the bilge & wooden compression posts & Catalina smile can develop in older models. Can easily be bought under 20 k & fix up as you go along. 1990's models are much more pricey, but redesigns may be worth it. The Catalina 309 is the later, upgraded evolution of the C 30. The C 34 is better still, just the larger sister. They all share similar rigging designs & the Universal 25 3 cylinder engine which is a workhorse. Later C 34's switched to a keel stepped mast which is a lil tougher, and avoids wooden compression post rot problems all together. Most sailors would recommend starting smaller (C 30) & working your way up the ladder in size at is is warranted. The costs of a C 36 are the most prohibitve issue: cost to buy, insure, slip & maintain go up as the boat lengthens. You'll find that the hardest part of sailing a big boat is getting the big, beamy buggers in & out of their slip without banging you boat or somebody else! That's why its good to practice with a smaller boat & gain experience.
The alternative to purchasing is to daysail a friend's boat, rent / charter them to get a feel for what you want & like vs/ need. Good luck & enjoy the hunt.