Heavy mortar vs Field ordenance

One mortar cost 50 points Two mortars 100

Field ordenance with bombast cost 120

Mortar S6 AP-1 D2 Bombast S7 ap-1 D2

(Yeah, mortar are legends but... In non competitive...)

They are the same in rules, the only difference is the unit size and de 1+ of strenght

What do you prefer??