I'd say GMS.Though I am very experienced with CTF and suck at GMS,GMS more advanced.You can make 3D games as well and do a lot more features CTF can do.But overall they are both great.

I have GameMaker: Studio and it's cool to use. You get to learn code and things like that.

I have scratch (obviously) and clikteamfusion CTF is great is quite hard though, i went to a gaming course they used CTF they had scratch swell but we used CTF

define 
CTF is cool but is quite hard

set [ and scratch is coolv] to [100 ]

great scratchCTF is still greatyeah lol

Clickteam Fusion 2.5 is sooooo easy to use, it's easier than Scratch, there are extensions

Platform Movement Object

I tried to learn GameMaker Studio, but I couldn't get into it. I understand why a lot of people like it, but I couldn't figure out the thing for the life of me, even with tutorials.

I, however, love Clickteam Fusion. It's confusing at first, but once you figure it out, it allows you to create things quickly. I'm currently programming an RPG in it right now, and it's coming along wonderfully. There's an overworld, a turn based battle system, shops, and a leveling system.

I believe your statement of Fusion being limited is inaccurate. If you know how to use the software, you can do some pretty amazing things with it. I've seen many great games made with it.

Everyone has their preferences though, and if you like GameMaker: Studio better than Clickteam Fusion, that's fine by me. As for me, I am going to keep using Clickteam Fusion.

What about other game engines? Like Unity, Unreal, GameSalad and even Pocket Code?

And yeah i used CTF first, but then moved to Corona SDK, Unity and Game Maker: Studio