This may be a stupid question but given the choice between EGT and Wideband A/F monitoring, why would you not want to go Wideband A/F? Doesn't your EGT get affected by timing as well as your fuel mixture? This could muddy the waters when trying to determine whether you are running rich or lean.

I agree both would be best, but if you had to choose one, why not a Wideband A/F?