I like the portuguese ( spelling ) league as its really close with Benfica Porto Sporting And i must say i like to be benfica as i think they are the weakest team out of the 3 i think and its a bit more of a challenge
Cro league is pretty fun as I got a save with Dinamo and its always fun trying to get them high as you can in the champions league. But the max 4 foreigners on the field thing gets annoying. Oh and plus Kovac isn't in Dinamo in fm09.
Well if you are interested for a league where u can dominate and then champion's league will be a serious challenge , try Greek with Panathinaikos/Olympiakos/Aek(AEK lacks of money when other 2 got 10-15 milion budget) or Turkish with Fener. You will have a serious challenge trying to bring big names cause of low league reputation and in the same time you will be able to challenge semi/quarter finals on CL.
On the other hand if you are looking for a tought League without much chances for a European Cup try Irish, Hungarian,Polish or Bulgarian