Thank you all for all the info.

I think I started to get an idea how it all works. A long way to go though.

I notice that “starwood from AmEx” is very popular.
Doing my research I found that “Preferred Reward green card” from Amex also allows to transfer point 1 to 1 to 11 FF programs. Which is as flexible as Starwood card. It also gets you 2point per $1 is gas stations, supermarkets, drugstore. Of course it has a hefty fee of $110. but nobody seems to mention, this card on the forum. Is it not popular because of the fee or some other reasons?

Thank you