I upgraded arbs first because their combo with cannons is deadly esp if the war boost is active! They r pretty effective even now, nd will make things easier for u!
During ur trophy range mummy is more useful than wolf nd ogre! But by the time u unlock wolf lvl 3 nd join a alliance which boosts ogre/wolf, u ll be using the wolf or the ogre/wolf combo a lot! Boosted mummy will still be effective!
About the basic units, what oPelle said! (Archers do give me a headache at times because they r harder to manage nd highly vulnerable from side lane, but the tribal Archers r really strong)!
Knights: this is a crux unit! Soon u should join an alliance that has blazing Knights nd max them as soon as u can! Wolves+knights work like bulldozer, razing everything to ground in their path, esp if u hv good scream gear!
Frosters: They may seem weak! Nd they may disappear if a single volley from a skull tower hits them! But they r indispensable! Even without the boost they can be quite effective. Can be used with knight/wolf combo or even with boosted arbs/cannons!
But when boosted, they r a thing of their own! Whole raid is centered on them! One ice dragon at the right time nd even the most difficult situation may turn in ur favor! u can raid any base scroll free(obviously u will hv to hv good leadership/scream as well)!
And they r also indispensable in defense, so its always good to upgrade them at regular intervals! Though u can wait to max them after u hv maxed Knights/cannons/arbs or even Archers as a lot of mid lvl alliances will run the Archer boost but the froster boost will not be effective unless the alliance has at least 43 fiefdoms (I m not sure, oPelle’s wiki pages r pretty helpful with this)!