i try to put on paper my choices
the soviet gun-howitzer M1937 had many pros: range, good traverse and elevation but had a heavy cons the weight is the heaviest piece, more 2 time of lightest.
the british 5.5-inch: the weight go down of 900 kilos, but also the range go down of 700 meters (with a 7.3 kg lighter shell)
many howitzer (sFH 18, sFH 37,Mod. 37, Bofors export, Skoda export, M1) are in the 5.2-5.7 tons weight range whitin this i stay with the sFH 37 (t) this is 1.9 tons lighter of M1937, 1.5 km less range.
the soviet howitzers and the sFH 36 are lighter 3-3.5 tons and 4.5-5 km lesser range actually they are in a different category comparating with the ML-20.