The way I look at it is what is the average value of the guy we might obtain from that pick.
This is going to be a very mathematical post but that's the kind of person I am.
Lets assign a numerical value to different things, from a scale from 1 to 100.
Rielly - 80
Nylander - 70
Marner - 65
Gardiner - 55
1st overall(Matthews) - 90
2nd(Chychrun) - 70
3rd - 65
4th - 60
5th - 58
6th - 56
7th - 54
8th - 53
9th - 52
10th - 51
11th - 50
12th - 49
13th - 48
14th or below - 45(it's quite unrealistic our pick would be much worst that that, we'd need to make the playoffs)
Now lets take a guess at rough probabilities that we end up with each pick
1st - 10%
2nd - 10%
3rd - 10%
4th - 20%
5th - 15%
6th - 10%
7th - 7%
8th - 5%
9th - 4%
10th - 3%
11th - 2%
12th - 2%
13th - 1%
14th or lower - 1%
Now you probably disagree on some of these values or odds, which is fair, but this is how I value them.
To calculate the average value of our pick given all these possibilities and values, not gonna post all the math here, just the answer. I suspect most know how to do this, just multiply the value of the pick by the decimal odds we pick there(90 x 0.1 for 1st overall for example) and add them together
Which puts the average value of our pick at 61.75. Less than Rielly, Nylander and Marner, but more than Gardiner(and other players I didn't list)
I feel like some people go too far 1 way and say look that pick might be Matthews with a value of 90, it's the most valuable thing we have because it could end up as Matthews who has more value than anything we have.
I think TLeafsFan is going too far the other way, it could end up 7th or lower which all has less value than Gardiner(based on my made up values in my chart), and that's absolutely true, it could. But based on all the scenarios possible and all the values of those scenarios it's more likely than the picks value turns out to be more than Gardiner(and Kadri, and JVR who's I'd both likely have at 60's, etc, etc)
But yeah there's my long drawn out explanation of how I value things in my head. When they have an unknown value like I pick I think how the average value it would have in all possibilities.