well... the crossbow did it for me (a.k.a bowgun)
especially the rapid shooting one (it needs rifles 5) - its got me all up to wave 25 without a single death
oh, and i thought that the lazer ports are weak till i bought all of them at the same time ... although the best buys are the three in the middle because they are not so easily destroyed
easy xp :
after you research the archery tree
just upgrade ingame till u get elemental arrow
turn autofire on
go to work
return and finish the level for lots of xp
(work best on the level 8 for me ...)
well... its short enough to be fun while repetitive
and the weapons are all the same .. well.. almost :)
but still - great mindless fun for a while - which is great for a flash game
but still... one thing i couldnt understand... what does the yellow dots do ?
 "Elona Shooter"){kind=icon}
 "Medieval Rampage 2"){kind=icon}
 "Enigmata"){kind=icon}
 "Cargo Bridge"){kind=icon}
 "Orbital Decay"){kind=icon}
 "Artificial Junk"){kind=icon}
 "Epic War 2"){kind=icon}
 "Rage 3"){kind=icon}
 "Epic war"){kind=icon}
 "Pandemic 2"){kind=icon}