Overall, the ZDT Jr. is probably the best amp among all the tube amps you listed, although I haven’t heard the Mad Ear + HD. However, for your 32 ohm Grado, I wouldn’t recommend any of the tube amps above.
Most tube amps have a high output Z, which will cause distortion with low Z headphones like your Grado. IIRC, even the low Z output of ZDT Jr. is over 20 ohms. The lowest output Z among those is ironically the OTL Valhalla 2 in low Z mode (which is probably achieved with use of negative feedback), but the Val 2 still sounds better in its high Z mode paired with high Z cans like Sennheisers and it would be a waste of an amp to use with your Grado.
Honestly, although I can’t say I’ve heard the GH2 in particular, most Grado headphones I’ve heard, including the so-called flagship models, sucked. They don’t scale as high as many headphones that are a lot cheaper, and considering their house sound and low impedance, I found them to be a poor match with tube amps in general. I can understand some people may prefer them for rock music (although I would still take a more resolving and neutral can that hits hard), but even so, I don’t see the point in trying to use a tube amp with Grados.
My advice is to buy a better headphone (a good starting point is HD600/650/6XX/58X), but if not, look for a decent solid-state amp with a low output Z.