I wrote my first couple of games in Quest and have since moved on to Inform. I found Quest much easier to pick up and use almost immediately; everything is neatly arranged for you so you can create new rooms at the push of a button, you can see how to set descriptions and so on. All the simpler stuff was much easier to learn in Quest. The ability to automap was nice as well. However, once I tried to do more complex stuff I found myself running into real problems in Quest because certain things were very difficult if you didn't understand how the underlying code worked. For instance, in Jacqueline, Jungle Queen there was a bottle of wine that got you progressively drunken and would wear off, which I had to sort of kludge together out of counters and if-then statements and which could still break if people messed around with it too much. This would have been much easier in Inform; anything involving values that go up and down is. (I believe you can do that stuff in Quest too, it's just a lot less accessible, and I never really figured it out.)
Other considerations with Quest: it has a reputation for bad games which is partially a side effect of it being so easy to use (you can throw together a terrible game in minutes and publish it on the site, and people do) and I found that some people couldn't play my games because Quest only works on certain computers. Taking it all together, my experiences lead me to prefer Inform 7 in the long run, but if you're more comfortable with working with the code then Quest has some nice features, and the frustration factor of learning it was much lower.