the answers gunna be a bit bisaed asking on a maya forum
but i will be truthful

render: xsi, altho maya 5 is looking very nice for this
modelling-
polys: xsi
subd's: xsi
nurbs: maya
animatin: xsi
dynamics: maya
scripting: maya
texturing: maya
rigging: maya
skinning: xsi

but this is usually up to the user, the above is just the way I see it