The first species listed is always the mother (seed carrier) and the second is always the father (pollen donor). With Nepenthes, traits (both appearance and growing habits) tend to lean towards the mother, while in other genera like Sarracenia it's more of a 50/50 split.
Normally, I would say that robcantleyi x burbidgeae would theoretically lean towards N. robcantleyi, but it's been observed many
times that N. robcantleyi tends to make mostly (in my opinion) lackluster hybrids - for some reason, the N. robcantleyi never really expresses itself very strongly in its hybrid progeny, regardless if it is the mother or father of the cross. On the other hand, N. burbidgeae tends to make itself very well known in its hybrids - any plant with a parentage of those two species will probably look very strongly like N. burbidgeae regardless of what plant is the mother or father. From what I've seen so far, that certainly seems to be the case, although I suppose that someone will have to grow multiple individuals of the cross out to full maturity to really see.
Another thing to note - with hybrids, always expect a large amount of variability. For example, BE's cross N. spathulata x platychila. For the vast majority of these plants, the lower pitchers seem to strongly favor N. spathulata with their size, profile, and solid peristome color, with only colorful mottling to betray the N. platychila father. However, I have seen far fewer individuals that have impressive striping on the peristome in addition to everything else, a trait from N. platychila that the majority of the crowd missed out on. I suspect that if the reverse cross was done far more plants would have the persitome striping, while losing some of the traits of N. spathulata (such as the bold peristome and huge size).
N. aristolochioides always presents itself very strongly regardless if it's the mother or father. Any of its hybrids that you select will have the obvious influence of its unique pitcher shape, although it will be more prevalent in some individuals than others.
HeliamphoraWalnut wrote:N.aristolochioides hybrids are often smaller, and have smaller pitcher mouths.
Unfortunately, they don't look like aristolochoides that much.
nepenthes ventricosa x aristolochiodes
This may be a matter of opinion, but that sure looks a ton like N. aristolochioides to me. It's practically impossible to tell most of its hybrids apart with how similar to N. aristolochioides they look - the only thing ventricosa in that plant is the slightly reduced hump and perhaps a bit of the peristome.