Either the space marines or the Eldar since the Space Marines are going to be big in numbers and the hardest, we might want to get them out of the way first. On the other hand, Eldar are weak and puny in size and numbers, we could get rid of them pretty quickly and work on the tougher guys next.
Oi, Appledrink we should definitely kill the Panzees first, then we can orkify their weapons and vehicles to serve our WAAAGGH!
I says we stomps em' alls! Dis stratagerzing makes head hurt... but since dis is a de-mocratic ork'anization i says we WAAAGH da panzees. I likes to kills da panzees!
Oomans are pink and soft, not tough and green like da Boyz. They'z all the same size too, so they'z always arguing about who's in charge, 'cos no way of telling 'cept fer badges an' ooniforms and fings. When one of them wants to lord it over the uvvers, 'e says "I'm very speshul so'z you gotta worship me", or "I know summink wot you lot don't know so yer better lissen good". Da funny fing is, arf of 'em believe it and da over arf don't, so 'e 'as to hit 'em all anyway or run fer it. Wot a lot of mukkin' about if yer asks me. An' while they'z all arguing wiv each other over who's da boss, da Orks can clobber da lot
