Here's a small guide on the best places to go to unlock your weapons and items so you can use their true power/potential if you have any better than the ones posted feel free to add on. Also kills only count with the weapon or item equipped so use traps or techs to reach enemies out of reach. Also for those who needs materials use the following ids in all quest skyly, greenill, and whitill for any class.
Episode 1
Wrath of the Forrest Enemy count (Includes all Mothmant/Mothverts & Dragon/Sil Dragon) - 734
AOL Event (depends on doors and traps) 443 (solo)
In Defense Systems - 1,200 Plus the possibility of 2 photon drops and 2 Photon Crystals
Christmas Event - 540
Maximum Attack 1 Ver.2 471
Maximum Attack S 492 (more if you allow Bulclaws to attack)
TTF Ultima - 519 (more if you can freeze the Baranz/Garnaz before missile attack)
Max Attack U Forrest - 183 (but can complete quick for multiple attempts plus good place for farming mats quick)
Harmony of Despair Pt.1 - 1,628 (with swords and sabers for cast more for force rangers and humans who can use techs) Hard difficulty or higher unlocks part 2 for another 1,500 + kills and a photon drop chance
Cavern of Gloom 727+ (maze route with a material/grinder drop chance)
Strange Sightings 457+ (Multiple hildebears and hildeblues for material if greenill or skyly)
Lt33 Vs Ultima w1 392 (a unique spin on TTF and a mat/grinder chance for certain classes)
Episode 2
Max S Episode 2 354+ (Warning quest may freeze jungle seaside and mountain bosses may alter count and ids grenill, skyly can get mats)
Mysteries of the void- 1,200 (photon drop if all enemies killed in part 1)
Episode 4
Christmas fiasco 497 (Photon Crystal collection area)
Realms of War 529 (No items collection also 10k meseta pay in with 20 minute time limit)
MA4DMD 349+ (photon Crystal drop chance)
Fastest and most kill will come from Maximum Attack S (483 kills in 14 mins or less on average)
Slowest but the most amount of kill will come from Harmony of Despair (1,628 in 59 mins or more depending on class, power and defense)