The upside to something like the S5 (or SP20) is that it should be economically viable for a longer period of time when difficulty starts rising. The S3 will drop into "not paying the electric bill" sooner. My sense is that the last few months of "small to no" difficulty increases will end in the next couple months, and we'll see another ratcheting up of difficulty. I hope not like the brutal days of 10-20% increases every two weeks.
As always it depends on your definition of "best". None of the suggestions are obviously "perfect".
If you can get a ROI on s3 really nothing else matters. Upside of having better gear does not come into effect. Once they hit ROI they are making pure profit. If they can achieve pure profit quicker on S3 they should go there.
This is for very few and those with extremely low electricity. For them S3 might be the ticket. For most with normal electricity S5 and others are better.
