First, thanks for the SPS yesterday, (from when I post this,) I need all the help I can get. Now assuming you allow it, since your rules don't say otherwise; lets see if lightning can strike twice...lol

I find this question to be difficult as well since I try to keep my collection balanced so I have more options given the different rule-sets. Doubly so since I think meta play is boring and try to break meta teams when I think I can. Therefore, The only metric I can use to come up with a single favorite is art.

As far as the card art for tanks go, I think I like Phantasm the best. While I don't use it as much as I do Bone Golem, Every time I look at the card, I notice a new detail that I hadn't before that changes the way I see the image. I find that rather cool.