This is a subjective question, and at times controversial. Much depends on what kind of project you want to make.
I think it’s fair to say that Quest isn’t as popular as other IF tools. The two most popular tools today are probably Twine and Inform, where Twine is good for building hypertext choice-based IF, and Inform is good for parser-based “text adventures” (games that tightly combine puzzles into their story, especially inventory puzzles).
Quest occupies an in-between spot where you can build point-and-click text adventures. (It has a parser mode, but the parser isn’t as robust as what you can do in Inform, especially with all of the extensions people have written for Inform.)
I like point-and-click text adventures and I think there’s a huge opportunity there. (Detectiveland won IFComp last year!) But the problem is that I’m not aware of any Great Games written in Quest. Some of Steph Cherrywell’s earlier games were in Quest, and reasonably well received, but she decided to switch to Inform for her 2015 IFComp submission and she won that year. Detectiveland wasn’t written in Quest; it was written in Robin’s home-brewed system that’s not (yet?) available to the public. (I think Detectiveland could well have been written in Quest, though it would have lacked some of the UI embellishments.)
Ultimately, if point-and-click text adventures are your thing, Quest may be the best tool for you. Quest is the best tool to make a Quest game. Twine is the best tool to make a Twine game. Inform is the best tool to make an Inform game.
On the other hand, if you want to make money writing IF, almost nobody is making money based on Twine, Inform, or Quest games. In the choice-based world, Ink is designed for you to build a Unity game around it (you’ll need to be a full-blown coder to do this). At Choice of Games, we have our own language, ChoiceScript, which authors use to write choice-based interactive novels for us; we have a large enough fan base that we can offer to pay authors thousands of dollars in advance to write for us.
As for parser-based games, if you’ve got excellent technical chops, you can wrap up an Inform game into an iOS app and a Win/Mac/Linux app with tools that Zarf has provided, but it is Not Easy, and there’s no way to build an Android app (folks are working on it) which limits the market substantially. As far as I know, nobody’s making a full-time living off of the sales of their parser-based text adventures.