Sarah really hasn't been given a winners edit though has she? I feel for her if she is the winner, because the producers haven't shown the audience her as much as some others to have built as much fanbase and approval. I do think she has some appealing characteristics for Sam - easy-going (doesn't bitch about the others really) yet sophisticated, lives in Melbourne, wants to travel, is career focused.... she is kind of a mix of the other three in the things he likes in them. Their last date did have some chemistry in the kiss.
I haven't seen the screen-cap talked about but observing when watching it will be interesting to see why Heather goes if she goes 4th. Sam's eyes often gravitate towards her at the cocktail evenings and group dates. I also think she is one of few that he really seems to have got past the small talk stage with. I know we don't see all the date but the conversations with Lana seem very superficial (not in depth on topics, very first date small talk) And Sarah not much more even after three dates!
My bias is towards Heather I guess because I think any decent relationship that is going to last requires a friendship as well and chemistry, and they do seem to have that. From what they have shown they make each other genuinely laugh.
I am being that typical over analyser aren't I! lol