1. It does´t matter, as long as you get them to half a heart. Making a drop shaft is obviously cheaper then a crusher, but takes more space. For the killing the most efficient, at least time efficient is potions (health potions for undead mobs, zombies and skeletons)
2. you should be within a radius of 16 blocks (in any direction) from your spawner in order for mobs to spawn. If you watch your spawner and you walk away, you will see the flames go out as soon as you step on your 17th block distance.
In my opinion, the xp farm by Snocrash is the most efficient. It is 3 circular disks, and it exploits the pigmens behavior, and drops xp when all of them are aggroed at you, and they fall to their death = a lot of xp. So, I think fall damage is more space efficient, and cheaper then a crusher.
Yep, but I'll prefer Snocrash's farm then Impulse's. I tried his, and it worked perfectly fine, but the redstone is just a bit too much for me - not too good at that, and I tend to get more xp from Snocrash's.
And Docm's enderman farm... I didn't even find the end portal yet, although I use that in every one of my worlds...
For spawners, I generally find that a crusher is better than a drop, on hard anyway, as suffocation damage is not effected by armor, whereas drop traps can leave mobs wearing Feather Falling IV boots at almost full health. You still get the occasional mob that has higher lvl enchanted armor that isn't a 1 hit kill, but a lot less than with drop.
For collection point, just make sure you are within the 15 blocks, but also you want to get the mobs at least 10 blocks away from the spawner (not an exact figure) as soon as possible so that more will spawn.
2. What's the optimal distance your collection point should be from your spawner?
2. you should be within a radius of 16 blocks (in any direction) from your spawner in order for mobs to spawn. If you watch your spawner and you walk away, you will see the flames go out as soon as you step on your 17th block distance.
Here's the optimal way to XP grind:
https://www.youtube.com/watch?v=R_Oe9vdrz2k
Here´s another cool design for pigmen, i made this one in my world and it works like a charm:
For me, when it comes to fast xp grinding, this classic is still the best:
And Docm's enderman farm... I didn't even find the end portal yet, although I use that in every one of my worlds...
Well, this thread went kind of off-topic, lol.
Get Your Portable ID!
For collection point, just make sure you are within the 15 blocks, but also you want to get the mobs at least 10 blocks away from the spawner (not an exact figure) as soon as possible so that more will spawn.