I had a very low gear on the old HT, 20/34….. 😛 which worked out (according to Sheldon Browns scale) was a 15.5″ gear, which was ace for getting me up the steep stuff we have round here
So, when i first thought of going full suss with 1×11 i purposely stopped using the 34 and used the 30 sprocket giving a 17.6″ gear.
Now, i like to pedal up stuff if i can and opted for the 28 front ring as this gives me a little less than i had before @ 17.3 taking into account that i now have 650b wheels as well.
Basiclly, if you have reasonable hills and can climb then the 30t front will do, that way you will still have a nive top gear on the 10 sproket. If you have steep hills (like us) then the 28t.
BTW, even with the 28t front, i can still pedal just fine on road with the 10 sproket….
Hope my little contribution helps! 😛