Best path is Rika.

Lies, Saki is best path, and though Rika is potentially life threatening Saki's is pretty much a death sentance.

Rika has a low life expectancy of about 30.

Technically this is simply how long people with hypoplastic left heart syndrome currently are when it was caught during infancy, it's not definitive that she will die around 30. With Saki though, they don't elaborate on the type of spinocerebellar ataxia, some cases people live a full length life, while others die in 10-20 years. This makes me think they may make a good lesbian couple? Not having to suffer for to long with the loss of a loved one.
Also is it just me or does Rika having red eyes make you think she may also suffer from Albinism?

I like the couple idea

I think Rika is an albino (but that might have just been the fan route I read(if you want a link ask)), also judgeing by the fact Saki already needs crutches to move around I reckon she has one of the faster acting versions.

I'd defs like the fan route, both if you have :p.
Yeah didn't think much about Saki's crutches, though I wonder how you'd meet her since it was supposed to be in the art club, which you don't pursue without rin.
Rika make's sence because you end up seeing the nurse no matter what at the start of the game and if you run with emi.

wut? wut?wut?