Congrats kooter, you've now asked the most important question in fantasy hockey, which should put you on the path to being a
much better GM.
Value Over Replacement is the lens through which you need to evaluate this question, and that will vary substantially from league to league. In the simplest example, let's look at two different scenarios, both points only leagues:
1. 10 team league where you have 10F and 4D per roster
2. 12 team league where you have 12F and 6D per roster
The first thing to do is define the replacement player at each position, ie the player you could find on waivers.
League 1:
F - 10 teams x 10 F per team = 100 forwards "owned". With last year's full season stats, the #100 F scored 46 pts
D - 10 teams x 4 D per team = 40 defensemen "owned". Again, the #40 D scored 34 pts.
League 2:
F - 12 teams x 12 F per team = 144 F owned. #144 F was 39 points.
D - 12 teams x 6 D per team = 72 D owned. #72 D was 22 points.
So in this ultra-simple example, let's compare O'Reilly and Keith in both leagues, using last year's stats (for simplicity). Feel free to project them out for this year... that's not my bag, but you'd want to do it with next year's projections in order to assess who you want to keep.
League 1:
O'Reilly = 60 pts - 46 (replacement level) = +14 Value Over Replacement
Keith = 43 pts - 34 (replacement level) = +9
League 2:
O'Reilly = 60 pts - 39 (replacement level) = +21
Keith = 43 pts - 22 (replacement level) = +21
So in League 1, O'Reilly is the rational keep over Keith. In League 2, it's a coin toss and a judgement call based on the GMs in the league and how they value the different positions. In some other league, it'll be a no-brainer to keep Keith.
Because the replacement players are different in different leagues,
league configuration dictates player value.
This is the simplest example because it's just points and only F positions. But the same methodology needs to apply when you differentiate F into C, LW, RW, and when you expand just P to G, A, +/-, PIM, SOG, hits, blocks, PPP, SHP, GWG, FOW, etc, etc. The only other wrinkle in the latter case is that you need to normalize the scoring categories to have the same statistical weight... there are various techniques to do that.
So you're probably thinking "holy crap FHG, this is complicated shit just to decide whether I should keep D or F". Yup. You signed up for a format that requires this level of analysis to get right.
Luckily, answering this question in a rigorous, consistent, defensible manner is why the
Fantasy Hockey Geek website does this analysis for you, automatically, based on your individual league configuration. I encourage anyone to do this themselves because the process of doing it really boosts your understanding, but there are plenty of pitfalls along the way. If you're lazy, just roll on over to our site.