The more disparate the 2 varieties, the more hybrid vigor will be expressed in offspring, both parents contributing 50% of the DNA to offspring, the traits you desire may be recessive when bred once aka the f1 generation. More of those recessive traits will be on display in further generations of inbreeding, every generation is important in deciding what traits are either bred out or selected for in future generations until you achieve uniformity, which takes at least 6-10 generations. Inbred lines's that have acclimated to regions around the world and their climates are considered "landraces".
Ace seeds offers some pure sativa hybrids.
Malawi x Panama
Golden Tiger- (Malawi x Thai)
Purple Haze x Malawi
Sativa f1 hybrids offer pure sativa effects with more vigor/resilience than many offer if the vigor has been bred out of them.