My grots seem to have an affinity towards vindicators - they are the most reliable tank buster compared to everything else (I think they are 4/4 in the wrecking/exploding category).
Although I have used grotesques more with Urien (and his strength upgrade) in the list I still have good success in crushing tanks without Urien's strength bonus.
But I must premise this with the fact that they really only get to charge one vehicle per game before the either get charged or shot to death.
My method is simply flat-out and then sail them towards a location with multiple targets, approximately 6" away from each other. Let the opponent expend his shooting phase in trying to pop the raider and hopefully they try to wound the grotesques (saving my other raiders some fire). What do I care, they are T5 with FnP, a cover save and most of the time fearless.
As far as being charged after they pop the raider, who would dare? I have only had them charged once by Dante and crew and although I lost Urien, the haemy and grotesques prevailed in 2 assault phases (thank you flesh gauntlet).
Usually the opponent has tried to shoot so much that he really doesn't try to get away leaving me an easy charge distance because I do not have fleet. Infantry or armor I don't care, the Grotesques usually have enough pop to render their target weak on the strike back.
That is what I like most about this squad, it is flexible for most targets but you do have to watch out for some super elite cc deathstars.