SQ's Krisflyer is good for the PPS scheme, but NOT good for accumulating miles (unless for upgrading on SQ, which doesn't apply if your are flying F).

I'd go with LH and BA along with most others - though of the 2 you get more bang for your buck out of Miles and More.

Though if you are in the UK, and get the BA/Amex card and earn a 2 for 1 voucher, suddenly BA looks better as it effectivly halves the miles you need. Plenty more on that in the BA Forum.