There are 3 imbalanced match ups: ud>elf,ud>hu,elf>hu.
Just check winrates of top 10 players.So below are changes,which i think should be made many years ago.
UD nerfs:
1)destros
850—>600hp
devour 50/75—>15/25 hp/mana ; cd 7—>15 sec
2)statues
500—>300hp ; HP healed 10—>5 per second
3)nova,frost armor and nerub tower/main
make ms slow=2,5 sec and -25% at all levels for both units and heroes
4)DK
coil manacost 70—>85—>100
5)fiends
web duration 12—>4 sec
burrow cast instantly,but cd 0—>30 sec and hp regen 5—>3 hp per second
Elf nerfs
1)DH
manacost/manaburn 20/40—>40/80—>60/120
2)increase cd of staff,reduce ms of dryads,but give them 300 manapool,make fairies 3 food,but increase their hp,talons fairy fire duration 70—>20 seconds,cyclone 20(6)—>10(3) seconds,nerf moonwells little bit
HU nerfs:
1)BM
sifon mana cast requirements 10—>50 mana,mana drained 15/25/40—>10/20/30 ; duration/cd 6/6—>5/10,range 800—>600
2)tanks 700—>500hp
3)spellbreakers hp 600—>500,spell steal manacost 75—>100
4)sorcs slow 55%—>25%ms,duration 60—>10 sec,manacost 50—>100
5)priests inner fire manacost 35—>75,duration 60—>30 sec
6)nerf gyros little bit
Orc nerfs:
1)SH healing wave manacost 90—>90/100/110,hex duration 15(4)/30(5)/45(6)—>10(3)/15(4)/20(5),serpent ward hp 90/165/200—>100/125/150
2)shamans nerf all skills
3)rider net duration 9—>5 seconds