I use either a 90/14 or an 80/12 depending on the thread, topstitch needle. I've been using titanium and they do seem to last longer.

Watson

When I use a thick thread like Connecting Threads Essential cotton I use a 90/14. Usually I use a size 70 when using Aurifil or any thread higher then 50 wt 3 ply. You really have to know thread weight and ply and type that goes with what needle size and what application it will be used for. It's another side of sewing that is important to understand.

I use a 14, but I stay away from titanium needles. A repair person told me they do break less often, but can damage your machine by not breaking. I rather just replace a needle then send machine in for repair.

I use 16s for quilting, also. They are big enough not to break very easily, and if they leave big holes, they close up again fast enough.

I use 16 for quilting. When I try a 14 there is a lot of thread breakage as I go over seam allowances. As soon as I change to a 16 it stps.

80/12 for piecing and usually a 90/14 for quilting. Although I have been known to use the 80/12 for quilting (usually FMQ) if it's already in the machine. My Bernina in particular seems okay with the 80/12 for quilting.

I wish repair people would get on the same page to what they are telling people. Two techs told me the titanium needles were fine to use, they stay sharp longer as they were titanium coated not made from it so no harder then regular needles.

My service tech lady who is a Pfaff expert gave me the tip that the 80/12 works best with my Pfaff. I found this to be true after I decided to take notice. I also use the Topstitching or Microtex varieties. I continue to use the 80/12 with quilting as it is still the one that works best. I use Aurifil or So Fine thread.
Please note this is the quirkiness of my Pfaff.

90/14 topstitch for all quilting/piecing. There are some threads that require the Microtex needle. Most threads work fine with the 90/14 topstitch. I am thinking of trying the 100/16 on a top with lots of seams....the holes will shrink when washed.

It depends on the thread size, type of thread and fabric being sewn on.