Here is where personal opinion comes into play. A genre or formula that you enjoy is probably unique compared to everyone else. Everyone is different so it is only natural to assume this. For me then I enjoy a lot (and has seen my fair bit of good and bad) so I can sorta make out what I like the most. A large margin of what I want to see comes from my mood but there are some basic blocks I can put them in.
For comedy/romance I really think that Seto no Hanayome is a prime example of the genre. What makes it special for me is the fact that the comedy never really out shadows the romance (as much as people think so) but rather is a tool in order to get the story moving and offers development. I love seeing character development, and the added comedy factor while doing it is a plus. The case size is also important as too many would just mean that some characters ultimately fade into the background. Not to big and not too small - SnH has a perfect balance
For action/suspense Gurren lagann wins my prize for being an anime that every other of its genre should be setting an example against. I'm not saying that all series should be as GAR as this but they "action" and drama is just top notch. Suspense enough to leave you biting your hands off waiting for the next ep and surprisingly has more emotion that a lot of other so called "romance" series out there. Manly tears are the best kind
For me I guess that I just enjoy watching series that does surprises well and for this even the legendary love-hate school days is high up there in my list. Being predictable is overrated but some series do handle it well (like the recently finished Night wizard).
A type of genre I really can't stand much are the horrible slow moving ones...or even "soothing" ones as they always make my mind wonder off into the land of sheeps...and being tired doesn't help either XD