gears: MTB and hybrid

Hello,

I have a MTB and a hybrid. They have similar gears: 42/32/22
chainrings and 11-30 cassettes. The hybrid's highest gear still
feels too easy (because of the tires with less resistance?).

I am thinking of installing a 48- or 52-tooth chainring on the nybrid
to get better workout (or more flexibility). Is this a
good idea?

About the specifications, I think I will need 104mm bolt circle
diameter, 4-arm chainrings (the originals are Shimano Alivio's).
Which set-up is better: new/42/32 or new/32/22? I suppose the latter
is easiest to work with, though the 22 chainring is hardly
useful.

Thanks.

Andy