I'm not sure, I want to say Goff will do better. But, Sam had a fantastic rookie year. Goff will have a better team around him, but the division is better than when Bradford was a rookie (remember the Seahags won with a 7-9 record). They both had great running backs. Both will have unproven WR core and offensive lines (though I think both are better now than they were in Bradford's rookie year). As much as I didn't like Shurmers offense, it did play to Sam's strengths. I just don't know what to expect with our OC.
To me, the biggest difference is the level of competition. Bradford played in a historically bad division. The NFC West now is one of the best in the NFL with some great defenses. I think Goff will end up the better player, but Bradford might have better numbers their respective rookie years.
While this is intelligent, reasoned, and logical analysis, I think you're ignoring the trend of statistical inflation since 2010. It's crazy to think about because 6 years is such little time but things have changed greatly. After Bradford's rookie year in 2010, Bradford was first all time in completions and pass attempts. He was second all time in passing yards. He was fourth all time in passing TDs. Bradford's QB Rating was top 10 all time. These numbers are all among rookie QBs.
Since Bradford's rookie season, three QBs have posted 4000+ yard passing seasons.(obliterating Manning's record) Two QBs have posted more attempts. No QB has yet broken his record for completions but a couple came close. Nine QBs have posted more than 18 passing TDs. Ten QBs have posted equal or better QB Ratings than Bradford's.
That's insane. Bradford was fourth all time in rookie passing TDs in 2010. Between 2011 and 2015, nine QBs bested that mark. Think about that for a second. Insane.
Since 2011, 15 rookie QBs have passed for more than 2000 yards. Of those 15 QBs, 10 posted QB Ratings equal to or higher than Bradford's. That means if Goff is only average for that group of rookie QBs, he'll posted a QB Rating higher than Bradford's. Jameis Winston and Marcus Mariota went #1 and #2 last year. Winston posted a 4000 yard passing season, put up 28 total TDs (22 passing and 6 rushing), and a QB Rating of 84.2. Mariota posted a QB Rating of 91.9 and put up 22 total TDs (19 passing, 2 rushing, and 1 receiving) in only 12 games. Mike Glennon, a 3rd round pick who is now backing up Winston, put up 19 TDs to 9 Ints and a QB Rating of 83.9 in 13 games as a rookie QB.
Rookie stats have taken off since Bradford's rookie year. That's because of rule changes which have caused statistical inflation and evolving schemes which have made it easier for rookie QBs to adapt to the NFL.
Simply put, even if Goff performs relative to his peers at the same level as rookie Bradford, his final numbers in 2016 will still be better.