I agree that as a member of SPG I have 9 out of 10 been upgraded to a suite. Compare that to The Marriott where 2 out of 10 I have been given a suite. Sure I get a Conceirge room but a suite I don't remember the last time!
The only reason I stick with Marriott is Corp. Policy. But for Pleasure stays Always SPG!
And yes it does matter who checks you in... I always try and be extra nice