Of course, when someone asks that question, the proper response should be, "I don't know, what do you have now and what do you shoot?"
I'm not a professional - though I did some pro work in the past, and for seven years was one of the co-owners of Hong Kong's PASM Workshop photo studio, shooting musicians, models, head shots, and events. I'm someone who recently sold off all my Nikon gear and went with Fuji and I'm not looking back.
The most demanding stuff I shoot these days is bands - mostly independent musicians playing in small dark clubs in Hong Kong and Manila. I also love to shoot just general purpose walking around in Manila and Hong Kong kinds of stuff, and also portraits of friends.
I have the X-T2. So far I have 3 prime lenses - 23mm F2, 56mm F1.2, 90mm F2. I love them all.
I also have the "kit" lens, the 18-55mm F2.8-F2.4. I wanted to get the 16-55mm F2.8 but was trying to save some money and concerned about the weight. The 18-55 has consistently surprised me (in a good way).
What I'm thinking about:
27mm F2.8 lens because it's tiny, relatively cheap, and while not in the top range of Fuji's lenses would likely be "good enough" for my purposes - something small and compact, making it easy to toss my camera in a day bag for walking around.
60mm F2.4 because a macro lens would be useful for me - I've got a lot of collections of little stuff that I'd like to document.
18-135mm F3.5-5.6 lens so that I'd only take one lens with me when traveling, albeit a big one.
Any thoughts on any of these choices? Are there other lenses that I should be considering? I'd love to have the 16-55 F2.8 and 50-140 F2.8 but those are both out of my budget for now.