I'm confused, shall I go for an onroad engine, lose some low end torque but gain top end power or shall I go for a buggy for a vise versa effect?? Is there an engine in between?

I saw some companies offer Rally engines, GRP, NOVAROSSI etc, however from the specs, they are very similar to onroads but with bigger cooling heads.

Please help... I'm looking for the BEST engine for rally, no matter the cost.

The car is BMT 081 RALLY....