Calculating a monster's 'score'

Like AngelSL said, all of the above would be great methods, but are time consuming and tough to do. The following formula works well for me in an excel spreadsheet that I have. It uses a value called "spawn factor" that helps the mob data you are asking for be a little more accurate. "Spawn Factor" is basically a quick estimated calculation for "time attacking mobs/time walking around a map", it estimates Fiel's above suggestion quickly and without extraction data.

Here is the formula:

"Monsters Score" = (Mob XP/(Roundup((Mob HP/Averge dmg of your main atk)/hit rate%))*Spawn Factor

Where:
hit rate % = % of time you hit a mob vs. miss a mob. (There is a well known formula for this in Dusks formula compilation)

"spawn factor" is as follows:
If hits per kill > or = 3 then "spawn factor" = .7
if hits per kill = 2 then "spawn factor" = .5
if hits per kill = 1 then "spawn factor" = .3
If mob is a boss then "spawn factor" = 1

It is not perfect but if you calculate the formula for all mobs in the game and then rank the values, it will get you the information you want. Let me know what you think. I will post the excel spreadsheet sometime soon if you are interested. It already has all of the mob data in GMS loaded so all you have to do is enter your ACC and Avg Dmg for main attack and it will spit out the mob ranks.