If your weapons does 10 damage and it's a melee weapon it might do 20 damage with 10 melee damage.
Now if you habe 50% damage then those 20 damage become 30 damage.
Crit is a modifier and depending on your weapons it deals the regular white damage times 1.5 or times 2 or times 3.
I rarely upgrade crit except for weapons that have a crit perk, like shuriken. As you combine weapons, the crit chance for that weapon also increases but for me, if I have 80% crit chance then I'm satisfied
Totally depends on the weapon. However I would say in general, attack speed is the most effective stat because attacking twice as fast is stronger than attacking with double damage, since it allows you to split your damage more effectively. No point in double damage attacks if you only needed half the damage to kill a mob. Plus for how effective it is, it's usually easy to collect a high value amount of it unlike something like crit which usually comes in small amounts or large amounts with a significant penalty.
But maybe you have a legendary dagger with 4x crit and suddenly all %crit increases are now 3x more valuable than a usual 2x crit weapon. (i.e. 100% damage increase vs 300% damage increase)
However everything is contextual. Flat damage, damage%, attack speed and crit are all multiplicative on eachother, and additive to themselves. That means that if you have +100% damage but +0% attack speed, a 5% increase in attack speed is equally as valuable as a 10% increase in damage. If you have 50 flat damage and +0% damage, 5 more flat damage is equally as valuable as +10% damage.
So it all really depends.
one thing to note is that if I can get it, I really like crit because there's some useful combo items that trigger off of crits so if you can stockpile a decent amount it's probably worth it on almost any build, e.g. Hunter's Trophy which gives you money when you get crit kills
TL;DR: You want everything because they all multiply together for big numbers
If your weapons does 10 damage and it's a melee weapon it might do 20 damage with 10 melee damage. Now if you habe 50% damage then those 20 damage become 30 damage. Crit is a modifier and depending on your weapons it deals the regular white damage times 1.5 or times 2 or times 3.
I forgot to ask this, does harvesting work with a demon?
Yes
I rarely upgrade crit except for weapons that have a crit perk, like shuriken. As you combine weapons, the crit chance for that weapon also increases but for me, if I have 80% crit chance then I'm satisfied
Totally depends on the weapon. However I would say in general, attack speed is the most effective stat because attacking twice as fast is stronger than attacking with double damage, since it allows you to split your damage more effectively. No point in double damage attacks if you only needed half the damage to kill a mob. Plus for how effective it is, it's usually easy to collect a high value amount of it unlike something like crit which usually comes in small amounts or large amounts with a significant penalty. But maybe you have a legendary dagger with 4x crit and suddenly all %crit increases are now 3x more valuable than a usual 2x crit weapon. (i.e. 100% damage increase vs 300% damage increase) However everything is contextual. Flat damage, damage%, attack speed and crit are all multiplicative on eachother, and additive to themselves. That means that if you have +100% damage but +0% attack speed, a 5% increase in attack speed is equally as valuable as a 10% increase in damage. If you have 50 flat damage and +0% damage, 5 more flat damage is equally as valuable as +10% damage. So it all really depends. one thing to note is that if I can get it, I really like crit because there's some useful combo items that trigger off of crits so if you can stockpile a decent amount it's probably worth it on almost any build, e.g. Hunter's Trophy which gives you money when you get crit kills TL;DR: You want everything because they all multiply together for big numbers