Pro mealy - the very clean underparts, white wing bars, limited red wash to chest, lack of obvious eye ring, impression of a supercilium, etc.
Pro lesser - browner upperparts, no obvious white rump on few shots I got that show back (although appears unstreaked?), structure not outside what you'd expect for lesser (but not outside range of mealy...), some possible hints of buff in wing bars, etc.
The last picture shows brown rump which would be very unusual for mealy. The first shows contrast between brown chest and white belly so Lesser Redpoll. The color of wingbars is not too good feature as all three, Lesser, Mealy and Arctic (exilipes) can show it.