Can't find which one it is.

H? H2? H3?

I'll be using an MK110 for the upper.

Can anyone help?

H2 equivalent weight is standard.  If you are using a can, they recommend the H3 (any H3) or even H4 (PWS produces).

Thanks for the info.

I went with the H4. Here it is. Pics aren't the greatest.

H4 for dedicated suppressor use only. H3 for suppressed and unsuppressed use. You may experience cycling issues if using H4 with the suppressor not attached. Use the appropriate gas setting while shooting suppressed #3 for crappy ammo, #4 for quality 5.56 NATO.

I personally use the PWS H3 buffer in my MK110 (suppressed and unsuppressed) so I don't have to worry about any cycling issues no matter the situation. I've tested about a dozen different types of ammo (Tula and Wolf included) and haven't had any issues.