In mud ags are better,but,,if you have loaded r4's and 4wd,you won;t probably get stuck,unless its serious mud,believe on ice,r4's would be better than r1's,,and can tell you after last winter,loaded r4's and 4wd,work very good in 2 ft snow.
R4'S give you a more stable platform on sideling slopes,and don't track near as bad in places you don't want tracked.