When Starwood & Marriott start their new program on 8/1, you will be able to transfer 60K Starriott points (=20k SPG points currently) to 25K Alaska miles. The new transfer ratio is unchanged from current levels since any SPG point will become 3 Marriott points in August.
If you have enough Marriott points (including your 1 SPG:3 Marriott conversion + 1 UR: 1 Marriott) to redeem a 270K 7 nt travel package before 8/1, you will receive 120K Alaska miles + certificate good for a current Cat 1-5 Marriott hotel.*
With SPG airline transfers right now, to get 120K Alaska miles would take 5(20K)SPG = 100K SPG points (actually giving you 125K Alaska miles).
If instead, you use 270K Marriott points (= 90K SPG) good for 120K Alaska miles + aforementioned hotel certificate, you'd still have 10K SPG left over which you can still transfer to Alaska and get 10K Alaska miles, for a total of 130K Alaska miles. Nutshell: more miles. And currently SPG points are on sale until 7/20. But redemption has to happen THIS month and I would not wait til the last minute. The new travel packages starting 8/1 are insulting compared to what they are right now.
Alaska has a credit card issued by BoA, I think the signup bonus right now is 30K miles.
If you've determined that Alaska miles are your best bet, the current Marriott travel packages are the best way to get those miles right now.
*lots of unknown about what will happen to that certificate after 8/1. Some people who are doing this are considering the certificates mostly disposable since the miles transfer is the big winner with the travel package. If you view it that way, then whatever value the certificate has will be a happy surprise on 8/1.