knights are cool if you plan on playing for a while and spending a few $$, but they really shine later game.
archers and mages deal damage faster, but lower d and hp usually.
i play mage and i like 1 hitting enemy troops and other classes lack high magic D so that also helps me in duels.
-basic strat would be try not to level troops unless you absolutely have to til griffs, then once those 29-30 start saving for lvl 40 knights, i hear you need 11 mil daru. (i didnt do this and wish i had now)
-get full set lvl req 20, use that until you get lvl 35 set from arena, then that til 45.
-save crypt keys until you hit at least level 50 in catas, thats where lvl 2 gems start dropping
-get farm level 30 soon as possible, try only to steal superior seeds until it gets late on server clock and you have not used all yet.
-spam spam spam for farm friends until you have full friends list, you can delete crap friends later, this helps you level your farm and more ppl to steal from.
-try to stay in the lvl 30-39 BGs until warrior rank
-try take only purp/orange bounties til late in day, then just do em
-usually as courtesy i dont steal ppls XP plants,