There has been a lot of debate on here as to whether drafting Malcolm Subban was a good idea. The debate is not whether he is good, but whether drafting goalies, especially in the first round, is a good idea. Some of the most respected prognosticators and evaluators on here - NaS and Stanley in particular - are very against the drafting of a goalie. It has been mentioned that forwards are the safest bet.  Some list have been given, probability incorrectly calculated, busts mentioned and successes shown, but what are the actual numbers? Well,

Probability of a 1st round pick playing at least 200 games:
Forward: 62.5%
Defence: 64.5%
Goaler:   44.7%

As you can see forwards are somewhat more likely to make the NHL for any length of time than goaltenders, while blue-liners are actually the safest 1st round choice without actually considering the particular player. When you get into the second round the numbers reverse:

Forward:  32.1%
Defence:  18.0%
Goaler:    33.9%

After the second round the probability of a pick making the NHL drops significantly, with goaltending being the biggest drop.  Few 3rd rounders make it and that is the same for the remaining rounds. Over 50% of all goaltenders who make the NHL come from round 1 or 2.

So goaltenders in the first round is the worst choice, in the second round the best choice.  There is a reasonable chance of success when drafting a goaltender early, but not quite as good a chance as with a forward. The other issue is the idea that goaltenders develop later. This argument was also used by someone last year RE:defence to say drafting Dougie Hamilton last year was a mistake. Truth is, goalies take a litte longer to make the NHL, but not much.  Average rookie age:

Forward: 22.6
Defence: 23
Goaler:   23.6

We tend to think of forwards bursting onto the scene at 18 like Crosby or Stamkos or Seguin, but the reality is that's rare and only common among 1st overalls. Most forwards establish themselves later and only 6 months - 1 year before the defenders and goalies. Since UFA status is determined by both age and at least 7 years experience, a player starting one year earlier is of no true advantage to the drafting team (unless they are an absolutely brilliant 18 year old, but even then the team loses a year of the player at 25 - in their prime). Jordan Stall will be a UFA at 24 while the Bruins will hold the rights to Tuukka Rask until he's 26.

Drafting Malcolm Subban may or may not have been a good choice. There is a significantly better rate of success in drafting forwards or defence in the first round while goaltenders are the better choice in the second. This was a late 1st rounder and the Bruins did not have a second rounder. There is a fairly reasonable chance that the pick will be successful based on history. In a Bruins fan's evaluation of the pick I would say the big question would be which would you choose:  a 62% chance of getting a forward to play 200 games or a 44% chance of getting a goaltender to play 200 games.