I was bored, here's some data on the fastest leveling builds. Take this data with a grain of salt, it's just data and doesn't necessarily indicate how powerful a build is, just how fast the people playing it are leveling their characters. This doesn't include characters from the start of the season, just the last half or so of patch 2.4. Hopefully the information is interesting and can inform tier lists & decisions going forward.
Fastest* Time to 100
* actually 2nd or 3rd fastest with over 10k kills, because some times were rushed or extremely twinked.
1. Summon Barb (3:10)
2. Werewolf (3:28)
3. Clawsin (3:42)
4. Holy Melee Pala (3:54)
5. Summon Necro (3:55)
► Show Spoiler
6. Nagisin (3:56)
7. Bloodzon (4:04)
8. Melee Sorc (4:09)
9-10. Mana Sorc & Totem Nec (4:12)
11. Javazon (4:16)
12. Banshee Druid (4:17)
13. Cold Sorc (4:18)
14. Werebear (4:19)
15-16. EQ/GT Barb & Neutraldin (4:21)
17. Lightning Sorc (4:25)
18. Unholy Caster (4:28)
19. Unholy Melee (4:36)
20. Wereowl (4:38)
21. Melee Necro (4:46)
22-23. Spearzon & Whirlwind Barb (5:01)
24. Holy Caster Pala (5:02)
25. Fire Sorc (5:11)
26. Psisin (5:15)
27. Scorpion Blade (5:17)
28. Bow Druid (5:22)
29. Stormzon (5:36)
30. Poison Sorc (5:40)
31. Poison Druid (5:47)
32. Malice Necro (6:05)
33. Bowazon (7:00)
34. Crossbow Necro (7:11)
35. Trapsin (8:17)
Fastest* Time to 120
* 2nd fastest with over 25k kills
These are twinked times but aren't record setting. Lynderika has done it in 5 hours on clawsin before, and mortimer_85 rushed RollsRoyce to 125 in under 1:30.
1. Javazon (6:04)
2. Werewolf (6:46)
3. Summon Necro (7:25)
4. Summon Barb (7:28)
5. Holy Melee (7:58)
6. Unholy Caster (8:08)
7. Stormzon (8:19)
8. Lightning Sorc (8:34)
9. Whirlwind Barb (8:41) [all kinds - phys, poison, other procs if anyone is playing ice lance or anything]
10. Wereowl (8:49)
► Show Spoiler
11. Unholy Melee (9:15)
12. Psisin (9:23)
13. Neutraldin (9:34)
14. Cold Sorc (9:40)
15. Mana Sorc (9:41)
16. Scorpblade (9:42)
17. Werebear (9:50)
18. Clawsin (10:02)
19. Melee Sorc (10:04)
20. EQ/GT Barb (10:07)
21. Totem Necro (10:21)
22. Bloodzon (10:41)
23. Melee Necro (11:14)
24. Banshee Druid (11:24)
25. Nagisin (11:48)
26. Poison Sorc (11:51)
27. Fire Sorc (12:56)
28. Bow Druid (13:04)
29. Bowzon (13:06)
30. Malice Necro (14:41)
31. Crossbow Necro (14:46)
32. Holy Caster (17:57)
33. Spearzon (24:02)
Not listed (0 characters in dataset): Poison Druid, Throwbarb, Trapsin
Median* Time to 100
* with between 10k and 20k kills, to remove characters who were rushed or spent a lot of time farming inefficiently. builds with <12 characters not ranked
1. Melee Necro (6:03)
2. Clawsin (6:50)
3. EQ/GT Barb (7:08)
4. Wereowl (7:15)
5. Summon Necro (7:19)
► Show Spoiler
6. Totem Necro (7:34)
7. Summon Barb (7:39)
8. Werebear (7:40)
9. Scorpion Blade (7:42)
10. Neutraldin (7:44)
11. Werewolf (7:54)
12. Unholy Caster Pala (8:06)
13. Nagisin (8:12)
14. Whirlwind Barb (8:13)
15-16. Psisin & Unholy Melee Pala (8:17)
17. Stormzon (8:35)
18. Javazon (8:39)
19. Melee Sorc (8:52)
20. Bow Druid (8:53)
21. Cold Sorc (9:03)
22. Poison Sorc (9:15)
23. Bloodzon (9:24)
24. Lightning Sorc (9:28)
25. Bowzon (9:48)
26. Fire Sorc (10:56)
Unranked due to low player count (less than 12 characters at level 100+):
Seer Druid (5:36), Mana Sorc (7:07), Poison Druid (7:25), Holy Caster Pala (7:59), Spearzon (8:04), Trapsin (8:17), Crossbow Nec (8:26), Malice Nec (9:24)
Median* Time to 120
* with between 25k and 50k kills, builds with <10 characters not ranked
1. Psisin (11:39)
2. Neutraldin (12:44)
3. Whirlwind Barb (13:29)
4. Summon Barb (13:56)
5. Wereowl (13:58)
6. Clawsin (14:24)
7. Melee Necro (15:08)
8. Werebear (15:15)
9. Lightning Sorc (15:19)
10. Scorpblade (16:07)
► Show Spoiler
11. Holy Melee (16:21)
12. Werewolf (16:32)
13. Summon Necro (16:38)
14. EQ/GT Barb (17:05)
15. Totem Necro (17:16)
16. Melee Sorc (17:19)
17. Poison Sorc (17:22)
18. Stormzon (17:38)
19. Unholy Caster (17:39)
20. Bloodzon (17:44)
21. Unholy Melee (17:55)
22. Cold Sorc (18:11)
23. Javazon (18:27)
24. Nagisin (19:01)
Unranked due to low player count (less than 10 characters at 120+):
Mana Sorc (12:32), Banshee Druid (13:11), Wereowl (13:58), Bowazon (16:31), Fire Sorc (16:49), Malice Necro (17:01), Holy Caster Pala (17:57), Bow Druid (18:16), Crossbow Necro (20:43), Spearzon (24:02)
Not listed (0 characters in dataset): Poison Druid, Throw Barb, Trapsin
Arbitary Tier List (1-120)
Ranked by (2 * fast time + 1 * median time)/3. Keep in mind this does not take into account
anything past getting to level 120. No farming, no bossing, nothing about how strong it is when geared up, just pure leveling speed. Some builds like Scorpblade are significantly more powerful at higher levels than 120, and some builds that are really good for getting to Hell (like Melee Sorc and Melee Necro) are ranked lower due to their iffy performance from level 100-120.
Also keep in mind that some lower player count builds might be ranked higher than you might expect because they're played only as twinked builds or by people who really enjoy the build and got good at it.
S Tier (577 - 620)Summon Barb, Werewolf, Psisin, Javazon, WW Barb
A Tier (620 - 650)Summon Necro, Wereowl, Neutraldin, Mana Sorc, Holy Melee, Lightning Sorc
B Tier (650 - 720)Unholy Caster, Stormzon, Clawsin, Werebear, Scorpblade, Banshee Druid
C Tier (720 - 800)Unholy Melee, EQ/GT Barb, Melee Sorc, Cold Sorc, Melee Necro, Totem Necro, Bloodzon
D Tier (800 - 900)Poison Sorc, Nagisin, Fire Sorc, Bowazon, Bow Druid
F Tier (900+)Malice Necro, Crossbow Necro, Holy Caster, Spearzon