If you ask this question to the senior members of this forum, they would reply, Most of them are their favourites.. Owning a nepenthes is so intoxicating and addictive that one wants to have more and more and more.........
Having said that, I would start mentioning a few;
(highlanders)
N. macrophylla, N. Ovata, N. izumiae (black), N. jacquelinae, N. lowii, N. burbidgeae, N. densiflora, N. rajah, N. veitchii, and last but not least, N. muluensis (purple with white lids).
(lowlanders)
N. albomarginata
N. rafflesiana
N. ampullaria
and N. bicalcarata.
Gus
Gus