Kazzi
hard question, but for cats 60mm should be better, since You're still out of their comfort zone. I usually do close-ups from really close and shooting tonight's photo (will be there in thirty minutes) was hard, since I had to use a tripod standing on a chair with 60mm macro.
There is also PanaLeica 45mm f/2.8 OIS and I think it might be a great compromise, since it's (as all macros) an insanely sharp piece of glass - I took a look at lenstip.com reviews and Olympus is sharper at the edges, but in the centre they're almost identical. Leica has a much slower AF, though.
Satoshi T My cats allow me to close them. but they move very quickly. so I really need very quick focus and short working distance. ... so should I choose Oly 30mm?
Kazzi If You're not in hurry, I can ask for 30mm after weekend and compare AF speed of those two. AFAIK, 30mm is really fast.
Satoshi T Yes, I'm not in hurry. If AF speed is not so different, it can be selected by focal length purely :)
Satoshi T Question: When shooting cats from nearby, which do you choose 30mm or 60mm?