It's certainly a dilemma, and either way you should do some research!
I've found that local 'pros' can also be a mercenary for who will pay them the most which can be an issue. I've seen them not even bother turning up for winter nets and even training sessions during the season - absolute fail in my book. Yes they're playing at the weekend and contributing onto the pitch but I think in club cricket you need to have the atmosphere and good club people who contribute off the pitch as well. In an ideal world, you're looking for somebody who can full invest into the club.
Overseas wise, we've only ever had one bad pro since my time with the club in the past five seasons or so. He was a good quality standard of cricketer, but his attitude didn't match. Always moaning etc which doesn't set a good example for anybody! I think the attitude can be as important as the on field contributions.
In an ideal world you're looking for somebody who can contribute on and off the pitch, both performance wise and attitude. Setting an example for everybody including the Youth and being a good role model is never a bad thing in my book. South African's have always been good Overseas, both on/off the field. Australian's have varied.