Ultra is much easer it work with
Mono has more color choices,
Mono has the pigment in the adhesive,
Ultra had the pigment in the film
Each one has pro and con
Mono is with a doubt more difficult to work with,
I personally use mono because I have been working with it for a while and I love the color opacity
I can pretty good with it.
Some people use a ultra base with a mono trim
Because you can use the windex method over a nice base