Hi there. I'm from St. Vincent's so I can give you my best perspective, but keep in mind that it's very hard to judge other programs when most of it is based on hearsay. After I spew my thoughts, I ultimately suggest that you speak with residents from each program to get the most accurate information about their respective residencies.
First and foremost, I genuinely don't think you can go wrong academically with any of the Portland programs. All of them will provide great educational opportunities. All provide strong teaching and focus on evidence-based medicine. I also think the morale is good at all 3 programs (although I heard some unfounded rumor this year about the Legacy folks being less so, but that was the first time I ever heard anything of the like). I think there are differences in their personalities and each have pros/cons. That said....
Fellowship: St. V's has about 50% going onto fellowship. Never had anyone not secure a spot. The residents get to know the specialists quite well so they make individualized phone calls on your behalf when interview season comes around. I believe only a small number of people at Providence go onto subspecialize (their website notes the exact percentage); nontheless, that doesn't mean they can't provide a program that leads to successful matches. Rather I could only surmise that they attract more people interested in primary care. I have no idea about the Legacy stats on this issue.
Work-load wise, I know people at both St. V's and Providence work hard but they have night float systems in place and are considered very humane programs. I believe the same is true for Legacy, but I can't confirm it.
St. V's and Prov Portland are under the same hospital umbrella (the Providence system) so have many similar components and benefits. St. V's is on the west side of Portland and subsequently has a greater % of pts that have insurance. So in clinic, you may have ~50% of pts on medicare (giving you a large geriatrics population), ~20% w/o insurance or low-income, and ~30% with private insurance (ranging from blue-collar workers to high-ranking people at Intel and Nike). Prov Portland, based purely on location, sees a much higher % of the indigent population and subsequently deals much more with the psychosocial issues often associated with this population (alcoholism, IVDU, etc.).
St. V's is the only program that requires 3 months of ICU during year 1. This could be good or bad depending upon your interests, but you certainly get good at dealing with acutely ill patients and you do a ton of procedures.
I believe St. V's has the best clinic set-up for both educational opportunities and continuity of care because you have designated clinic preceptors that you work with each week and who know your patients so they can provide teaching that incorporates each individual's psychosocial issues. Both St. V's and Providence have paperless clinics (using Logician), but St. V's has been spectacular in configuring the program to maximize all it's benefits.
St. V's and Prov are both one-hospital programs. Legacy is two (Good Sam and Emmanuel). We one-hospital programs think we've got it better because there's no travel time b/w hospitals and your clinic is always on-site. Plus, the residents became more of a family since we see each other qd. Legacy sees their set-up as an advantage b/c you get exposure to 2 different work environments. So they both have pros/cons.
Ok, I've probably rambled for longer than you want to read!! I hope it help though. While you may have surmised from my writing, I think St. V's is great and I certainly am biased towards what they have to offer. However, I know that all programs are incredibly strong academically and they are worth checking out to see which is best for you.
Good luck.