logical reads vs. scan count
Here is the killer deal: it January it was costing $12k to buy 864*GB* of RAM. You can get a lot of bang for the buck by simply increasing the RAM of your server up to the point that you will never hit a physical read (after warm up, of course).

Other than that is really hard to give an black or white opinion about either of those data points you present. Sure plan #1 had most physical reads, but are you positive that all tests were done on similarly warmed up cache? Could it be that #1 warmed up the cache for #2, what is your test methodology to ensure all cases are considered on level ground? Even so, if you shell out $500 and double the RAM, would it matter any more? #1 does have the least logical reads...

But then #2 is probably benefit from a high DOP (that one scan can be parallel). Is the wall-clock time of #2 better that #1 after you added sufficient RAM?

How many of these plans run in parallel? Are there tens of queries requesting concurrently a significant memory grant for the hash of #3 and thus creating contention for the RESOURCE_SEMAPHORE? Is the #2 doing a sort and also requesting a memory grant? Will #1 work better since it requires no grant (at least from the info posted...)?

Is really really relative and the question you ask is more like finding one solution for a complex system of equations... there simply could be more that one solutions.

One things is sure: 8M rows should fit in RAM with plenty room to spare. Those physical reads are begging for some memory banks.