Big problem I see with free is while you don't write as much, it's still a huge time commitment given how fast I see some of those games move. You don't spend hours online keeping up, you fall behind those who do. Obviously not all games are like that, but when you get dozens of posts a night, if not an hour in extreme cases, it's nuts. I also kind of get the impression Freebis mostly the younger crowd and usually there isn't much in the way of plots, creativity, or planning. It's very pick up and go without formality.

Casual is actually probably the best fit for most people on the forum, this is where character sheets really start to come into play and some GMs get stricter about rules and expectations. There's the most players here, which means the most games and likelihood of finding something that interests you. However, with that comes a wide range of expectations and player skill/aims. You get anything from players who write at a free level who think there's a stigma for being in Free (which is unfair to think; it's what some people enjoy) while others write a constant couple of paragraphs or more and end up meeting Advanced requirements without either realizing it thinking it fits there. This leads to problems where you can have people in the same game with vastly different skill levels and expectations and conflict can stem from that. This is why there's that whole High-Casual tag to ensure consistency in player writing. 

Advanced isn't nearly as daunting as it sounds. If you can write two or three solid paragraphs you're fine. It's more geared towards story telling and character development and it can often read like a collaborative novel. Posting tends to be slower and it can be hard finding people to join your games given the relatively small player population, but a good, dedicated group can make a game last for years. It's the best fit for people who like being descriptive and have a hard time writing short posts because they have a lot they want to say or do within a post. Main problem with Advanced is it can move dreadfully slow at times, where players may disappear for a while because they don't have time to write or the will to do so because of the general length they write at can lead to writer's block, which can happen at any level, but when you have several paragraphs it can seem daunting. 

Either way, there's something for everyone and no "better" level. If you like it, go nuts.