If you use Qt you can buy a commercial license or use the LGPL license (see here). Since I'm not even sure there is a viable Qt 5 build which links statically that seems to be almost a restrictionless license.
I avoid using LGPL (actually, I avoid GNU licenses altogether).
The main problem, specially when considering commercial games, is that LGPL also allows the user to use a modified version of the library (free to use). By using the LGPL licensed resource, you accepted this. It opens a wide plain of possibilities for problems. Unofficial, hacked, versions of the library would float around the Internet. Still, if your game is single player, there'll be nothing to worry about. But by the time you decide to make it multiplayer and hacking start to affect the experience of other players, you won't be able to touch cheaters. If they stay inside the library interface, there isn't much you can do. You'll see that the cheaters will probably fall into a penumbra between your TOS and the restrictions imposed by the LGPL, that states clearly:
...
That sounds like an artificial problem for me. Having access to part of the source might or might not make it a little bit easier to manipulate a game, but if it is popular it will be hacked either way. Most TOS are pretty much useless in anyway should they ever come to be tested in a court anyway. If push comes to shove instead of banning your identified cheaters you can instead move them to the cheater-only server where the can play for the rest of their life with other cheaters.
That said, if your game is popular enough for that to even become an issue, buying a commercial Qt license should be extremely feasible, completing removing that particular issue.
Now, whether your work is an application or a combined work differs only if you link it statically. So, no static linking or you'll also allow, beyond the usage of modified versions of the library (despite of its purpose), reverse engineering and debugging. In other words, if you use a shared link you've got problems, but if you link statically, they're really worse.
Not being reasonably allowed to link statically is a well-known restriction of the LGPL. However, many games I see have important bits of code lying around in (well-known, often open-sourced) dynamic libraries which could be switched out just as easily.
I guess this was one of the main reasons SDL dropped LGPL in favor of zlib. It surely was the main reason I avoided SDL in favor of SFML and Allegro for so long...
Why would the Qt Project provide a commercial license? If LGPL was really a good license, there'd be no reason for them to provide a better one.
Of course being allowed to link as you want is nicer. At work we have been using our Qt license to statically link to Qt 4, but that was also a bit of extra work. Unfortunately I'm not sure something like that is currently possible with Qt 5 but I believe some work is happening in that area.
In my hobbyist endeavors I have often followed the path of complete static linkage as well (sometimes including assets) so that the project result was a single executable. That has a certain charm as well and a portable version of your application becomes trivially easy like that.
However, currently my internal pendulum has been swinging another way. Working with Qt adds a lot of baggage to the project but the games I'm interested in are by there nature less reliant on extremely high-performance eye candy and require more sophisticated UIs. Qt goes a very long way with QtQuick to offer a very thorough UI system that integrates well with OpenGL.
Also, should commercial exploitation of my hobbyist projects ever become an issue I'm pretty sure I could live with buying a Qt license in order to negate any lingering LGPL problems/possibilities/whatever.
