There are quite a few that I've noticed and thought, "oh, that's him again!", but I wouldn't call anyone a favourite unless I've seen him (or her) and liked him in three or more dramas, with a feeling that I really want more. I feel that otherwise I won't know for sure if it's really actor-appreciation or just character-appreciation, or if I just like him for his looks. ;)
So far, my favourites are:
Iura Arata*
Fujiki Naohito
Eguchi Yosuke
Matsumoto Jun (the only one out of these four I don't think is hot, even though he's kind of adorable)
These are the ones that I want more of; I want to watch everything they've been in, I'm waiting for new roles and eagerly hoping for subs, etc (why do not subbers like Arata's dramas/movies as much as I do??).
Other potential favourites are:
Abe Hiroshi
Kitamura Kazuki
Takenouchi Yutaka
Tsumabuki Satoshi
* His MDL profile still calls him Arata, but the fact is that these days, he uses his full name as his stage name. You'll only see "Iura Arata" in kanji in the credits of recent movies/dramas, not "ARATA" like in the older ones.