The best Hybrid DK skill build?

 Old School Guide Style!

Lv70 - 1 Spear Fury (1)
Lv71 - 3 Spear Crusher (3)
Lv72 - 3 Spear Crusher (6)
Lv73 - 3 Spear Crusher (9)
Lv74 - 3 Spear Crusher (12)
Lv75 - 3 Spear Crusher (15)
Lv76 - Save 3 (3)
Lv77 - 6 Spear Crusher (21)
Lv78 - 3 Spear Crusher (24)
Lv79 - 3 Spear Crusher (27)
Lv80 - 3 Spear Crusher (Max)
Lv81 - 3 PA Fury (3)
Lv82 - 3 PA Fury (6)
Lv83 - 3 PA Fury (9)
Lv84 - 3 PA Fury (12)
Lv85 - 3 PA Fury (15)
Lv86 - 3 PA Fury (18)
Lv87 - 3 PA Fury (21)
Lv88 - 3 PA Fury (24)
Lv89 - 3 PA Fury (27)
Lv90 - 3 PA Fury (Max)
Lv91 - 3 Sacrifice (3)
Lv92 - 3 Roar (3)
Lv93 - 3 Roar (6)
Lv94 - 3 Roar (9)
Lv95 - 3 Roar (12)
Lv96 - 3 Roar (15)
Lv97 - 3 Roar (18)
Lv98 - 3 Roar (21)
Lv99 - 3 Roar (24)
Lv100 - 3 Roar (27)
Lv101 - 3 Roar (Max)
Lv102 - 3 ER (3)
Lv103 - 3 ER (6)
Lv104 - 3 ER (9)
Lv105 - 3 ER (12)
Lv106 - 3 ER (15)
Lv107 - 3 ER (18)
Lv108 - 2 ER (Max), 1 Spear Fury (2)
Lv109 - 3 Spear Fury (5)
Lv110 - 3 Spear Fury (8)
Lv111 - 3 Spear Fury (11)
Lv112 - 3 Spear Fury (14)
Lv113 - 3 Spear Fury (17)
Lv114 - 3 Spear Fury (20)
Lv115 - 3 Spear Fury (23)
Lv116 - 3 Spear Fury (26)
Lv117 - 3 Spear Fury (29)
Lv118 - 1 Spear Fury (Max), 1 Power Crash (1), 1 Extra (1)
Lv119 - 3 Extra (4)
Lv120 - 3 Extra (7)

Spear Fury does a little less than one of your 3 Spear Crusher hits, but it's much faster and reaches about 2/5 of your screen. As for Rush replacing Spear Fury... I've yet to see the max range of Rush in action myself (and if I have I must not have been paying attention), but you can't hit flying monsters with Rush very effective regardless, and Roaring flying monsters all the time is just a waste of pots (unless you have a healer of course). Also, you won't be maxing Rush any time soon so it wouldn't be useless to have max Spear Fury.