I'm changing all the time with what I use and what I do
I have just started on here now
http://minethatcloud.com/Seems pretty good and the people seem to know what they are doing
It's really hard to know where to stay and go so I always just look for deals that are the most suitable, I would'nt wanna stay to long on one place but I know alot of people
do, It depends really on how much hash I want to buy.
Until they provide some evidence of legitimacy, they're just another ponzi, as is cloudminr.io too by the way. With Cex.IO halting mining the other day and Hashnest halting mining today, AMHash and Bit-x are the only legitimate bitcoin cloud mining services left. There are also a few hosted services like KNC Cloud which offer fixed length contracts for say 6 months or a year.
As for why companies would offer cloud mining instead of just self mininig, they make a guaranteed profit up front instead of having that profit spread out over a period of time. For manufacturers services like AMHash, Bit-x and Hashnest, it's not really any different than selling miners.