I grow passionfruit, and I believe they are self-fertile. We've had most of our vines self-seed through birds and/or other critters. A couple weeks ago I bought a vine from Mitre10 though, that's absolutely thriving where I planted it. It's too young to fruit yet but...
Our fruit varies in size too. Sometimes it's huge and sometimes they are tiny. We don't tend to the plant at all either. It gets water when it rains, and the only fertilisation is maybe when my dog decides to plant her ass there, haha.
Fruit often shrivels or stays small when there is water stress. So keep up with water and fertiliser, and she should be right as rain.
Get any specie, really. Or get multiple different vines. Each vine has their own taste and that way you know what you like. Our vine (sadly don't know the species) is relatively sweet and low in acids. The one I bought from Mitre10 was advertised as a sweet black passionfruitvine.