To answer the OP- I think it depends on your needs specifically. Construct 2, in my mind, has the best UI and method of programming a game, hands down. However, don't plan on having a smooth release for your game with anything outside an HTML5 export. So if you plan on making a browser-only HTML5 game, there is absolutely no better choice than C2.
However, if you want to export to other formats - Be it Windows exe, Mac, Linux, consoles, and possibly even phone (IOS and Android as I've heard a good amount of issues come from the wrappers bloating the game's size, therefore affecting performance), you may want to consider other options such as GM. It is possible to use 3rd party sources to create something like an exe or app using wrappers, but as noted before, they tend to bloat the size of the project and affect performance. There are also many known issues with these 3rd parties where there's not much Scirra themselves can do. We're pretty much at those company's mercy if and when we encounter bugs trying to create something that honestly doesn't seem like was meant to be created using C2. Native exporters are a whole lot better, and that's something GM does have.
Personally, I don't like the archaic nature of GM; I can understand the appeal, but you can't seem to do much in that program without learning its' native language, GML. In that sense it's probably great for people who want to learn a simple programming language. For me and probably several other C2 users, we use this sort of software because we can't/don't want to learn an entire language to make a good game, so it kind of defeats the purpose. It's also not the most powerful language either. I've always kind of wondered why people don't just resort to Unity if all they do is program in GML anyway. Maybe it's a price thing, or it could be more difficult to program in Unity, I'm not 100% sure. Unless like I said, you're a beginner programmer looking to learn an easy language. Also, the level editor of GM drives me bonkers, but that could also just be me.
I can't say for sure because I've only just started trying it on the side, but if you want something similar to C2, but with native exports, Clickteam Fusion 2.5 may be a good option. From what I can find, this comes with some catches though. The reason Construct and Clickteam are so similar in appearance, as the story goes, is the dudes at Scirra liked what the program could do, but had become fed up with the constant issues that kept cropping up with it, making simple programming tasks a giant chore when creating games. I believe that's what got them started making CC as a more friendly alternative. So one would expect to find some very odd issues popping up here, and it wouldn't be quite as easy to get things done as it is in C2. Fusion is also more expensive if you want the ability to export to all its available platforms. It's upwards of $400 USD.
So the way I see it (And I've been pondering this for a while since it affects me as well). It may be good to have an alternative tool for if/when you aren't able to suit your exporting needs with C2. What you go with depends on what you need, but in my honest opinion, I don't see a whole lot of reason to go the GM route unless you're looking to learn an easy programming language!