There are way too many absolutes in this thread.
I like Hrivik. He plays a solid, strong, basic game with flashes of some nice skill. His development has been stunted by injuries. He was on an awful team for most of last year. Kenny G, in yet another example of his masterful coaching acumen, played him on the Pack 3rd line with plugs for most of the year. All of this worked against his offensive development, I'm afraid - but he continued to play his extremely solid 2-way game and, despite being a kid who could probably bolt to Europe, has remained committed to reaching the NHL. I think he bounces back and eventually has a career as an NHL 3rd liner.
Tambellini is a very different case. I actually think his family bloodlines may have worked against him in a "boy who cried wolf" kind of way. He was drafted as an absolute stick - you see different reports of his weight at the time, but if you look at his picture, he looks like Ichabod Crane. Meanwhile, the reports on his skills were glowing. You see things like "toolsy", "NHL level shot", "above average speed". The consensus was that he had top 6 talent... IF he could put on weight. He has trouble at NoDak and we're all down on him. He goes to the WHL and scores at a 1.25 ppg pace in a pretty small sample size. During the WHL playoffs he was tied for the team lead with 9 pts in 6 games (1.5 ppg obviously), so we start to have some cautious optimism.
Then he comes to camp last week and Leslie's reported that he's noticeably bigger. Twitter reports during the scrimmage say guys are "bouncing off of him" and he puts in a "dirty goal" that he basically forced into the net with brute strength. These are encouraging signs that he may be undergoing the kind of physical evolution that they were rolling the dice on seeing when they drafted him. But, he's still young, needs to keep growing and then we need to see what happens when he plays against men.
So, it's a classic case of a player who's close to reaching the NHL in a limited role vs. a guy with a longer shot at a bigger role. It's a balance obviously, but all things being equal I generally go with the latter - and in this case, where the first player trended down last year (even if it was not all his fault) and the second is trending up... Tambellini is the choice for me right now. Like a lot of our prospects after the top grouping, both of these guys could move as many as 6-8 spots in either direction by the midseason ranking.