In 120, I find that Plus-X is a good film to use with HC-110, because it tends to have rather brilliant highlights. Tri-X is much more about good midtones, which is what you want for most situations, especially with people. If you look at each film's characteristic curve, you will see that they differ a bit.
For landscape, Plus-X can be very interesting. But I can never manage to get it to my taste in 35mm--I haven't worked out a proper EI/dev time to avoid blown highlights (lazy, I know). So I stick to Tri-X in 35mm, because it suits my 35mm style more, and I use Plus-X in 120 because it suits my MF style more...