Dunlop Purofort Thermo Plus.... expensive but popular with farmers on account of their comfort and long life, but toasty warm and so comfortable that when they die I will convert them to slippers. Super grippy treads, steel toecaps and shock absorbing soles. Made of foamed rubber, they really are warm! Whatever they're made of shows better grip (even on hard smooth surfaces where tread pattern is unlikely to make a great deal of difference) than any other boot Ive worn.
Downside, the soles are rather wide, meaning those well-trodden foot-width gullies found in some caves may well catch you unawares....