Just for clarification, when you ask about gTLDs are you asking in terms of the new gTLDs that have been coming out or gTLDs as a whole.
If its just gTLDs as a whole, .COM is going to be your best and safest bet.
Cant really go wrong with a good keyword .COM or even .NET for that matter but I am pretty sure you already know that.
If your question is about the new gTLDs... that is something that we are still trying to figure out.
It is really too early to say that there is a concise approach to nTLDs.
Either which way, keywords are the ... well KEY!
A great keyword in pretty much any extension (as long as it makes sense and does not fundamentally clash with the extension) would be a great way to start.
Just make sure you dont pay too much in premiums (especially if it has a yearly premium renewal) because you may have to carry it for a while.