I have experience with FL Studio, Reason, and a tiny bit of Ableton.
I began with FL and, well, its an odd situation - it makes you feel pretty beast because of its flashiness and ease of use, especially when you have several good VSTi's. Now the problem is, when you're using FL, you tend to not really be aware of what you're actually doing, and a lot of it just seems like shortcuts - like using Grossbeat for a sidechain or a Parametric preset to do a fadeout and in. Plus FL tends to put out that sort of signature "Made in FL" sound. That said, FL Studio is great for a beginner who wants to get some experience making music, and there are people who use it very effectively, including Deadmau5 (amongst other programs, that is) and allegedly, Basshunter.
From my experience, I much prefer Reason. It has only 3 actual synthesizers. So you end up learning every aspect of a synthesizer, which is pretty critical in the creation of electronic music. Rather than just plugging in a VSTi sound that you like, you create the synth sound from scratch (although there are presets you can use). Drum sampling is still readily available though, and pretty intuitive. Reason is essentially packed with every feature necessary to create nearly anything you want (That is, besides recording live audio) but you need to practice with it and know what you're doing. Nearly everything in Reason is manual and is a digital representation of an analog item. So learning to use Reason is a great introduction to the world of modern music production, including the more precise aspects of it, which is, in my opinion, good to learn.