As much as I acknowledge that Garageband is a fully-featured DAW (Digital Audio Workstation), I would suggest trying out demos and trials of other DAWs to see if you find one which you prefer more. I say this because Garageband comes free with every Mac, and software that comes free with something is usually not as good as the same kind of software that you have to pay for.
You can still make great original music with Garageband I'm sure, but take a shot at some other DAWs like Cubase, Reason, Logic, etc.... Logic in particular might be a good idea since I'm pretty sure that it's quite similar to Garageband, so you won't have too much trouble making the switch.
If you like another DAW enough, then save up and buy it! It's a big investment but if you want to get serious about music then you'll most likely have to be prepared to dish out a fair bit of money in it. But hey, I know FatKidWitAJetPak uses Garageband and makes good music with it, and I'm sure there are countless others, so Garageband is a perfectly viable option if you're comfortable with that.
Also about FL having a bad reputation... it's unfortunate because it's a badass piece of software and doesn't deserve its reputation. I've heard that FL may be getting Mac support in the next version; if so, that would be a great piece of software for you to consider, especially since it's reasonably priced and comes with lifetime free updates, so you won't ever need to pay for future versions.