Melling camshaft

Are most makes of camshafts about the same? I am looking at a Melling cam but I haven't heard too much about them. They list a class I (200-215 duration) and a class II (215-230 duration), based on a .050 cam lift. The class I is refered as 'good idle' quality while the class II is a 'fair idle' quality. I'm not sure what the difference would be between a 'good idle' and a 'fair idle'. :help: I want something that doesn't sound like it's going to die if I don't give it gas. I've a 340 but it'll never see the track. Input would be greatly appreciated.