GO FOR IT, NEWBIE!!!

Hello everyone. I'm a beginner in Heroes 3. But I've only played against the AI before, and only played against other people about 5 times. I don't know any 1v1 strategies. I used to play WarCraft, so I understand that you can't get anywhere without strategies. Could you tell me which castles and heroes are the best in duels? Which castle beats which, and which doesn't. And in general, which version are people playing now, because I have 3 of them!