Tapajos Reds-definately the most red, both male and female turn rich deep red. Some shots by Tazz, Mt. Pike and co in the "Photo Shoot" section are good examples.
Cobras-Females turn pretty red, males less so.
Johanna-Red dorsal stripe that doesn't ade with mood. Reddish around head in some varients and individuals. Seems to be a special varient that gets really red, but I've only seen pics from Japan.
Xingu1-Females can get very red fins and when in the mood are very red bellied.
Semifaciata-Females have red dorsal stripe and red flanks.
Sp. Atabapo-Red heads and red fins, a lot of variation here as I've seen some that are very red and others that are kind of brownish and washed out.
Atabapo Fires-Jury still out on this one, definately get red fins and a red su-orbtal stripe.
All pikes when in breeding colors have red females-even xingu3s which are black get a lot of red when in bloom. Cintas, for instance which are mostly brown can be very red when in breeding form. But the above species are the ones that even when the fires of love have cooled still stay red to one degree or another.