Grille is definitely fun, the first truly good hit you can deliver via arty in the game. The downside is that it is SLOW like molasses. You have no prayer to escape or evade enemy scouts. Range is good too.
Hummel is an improvement on the Grille. It is both faster and carries an even bigger hit than the Grille. However, the Hummel is cursed by "drunken gunner" syndrome. Even fully trained gunners seem to get stupid on that tank, regularly enough that they call it the "Drunken Hummel Gunner" curse.
The eventual payoff, however, if the best arty in the game, so far. The GW Panther is god's gift to internet arty guys. It is fast, hits really hard... has a high arc and damn good accuracy if used correctly. It can go TD mode easily and the armor is good enough to let you take a hit and survive, even from another arty piece.