Unfortunately, the US conversion rate for Membership Rewards to Starwood is 3:1, not 1:1, making Starwood a poor choice for laundering Membership Rewards points into other programs.

You CAN do well in some cases with laundering Membership Rewards points through other programs...

For instance, instead of converting MR --> Hilton (1:1.3) consider MR --> Hawaiian --> Hilton (1:1:2).

Or consider Amex --> CO --> Amtrak --> United in order to get your Membership Rewards points into United (1:1:1:1, with a 25k/yr max).

Finally bear in mind all the partnerships that programs offer. So if you want to claim an award on UA without laundering points you can transfer miles to ANA or US. If you want to clain an award on NW, transfer miles to CO.