I really like both sizes.
For my breeding horses, I prefer A's and all are 34" or under except for one loud bay leopard mare (how could I resist?). I do own one arab grey filly who is AMHR and AMHA but may out grow her A's. The other 7 mares are A size. See our mares and fillies here:
Mares of Whinny For Me Farm
My stallions are 32" and 31". They are both AMHR National Top 10 horses in halter and AMHA Honor Roll horses in Halter. One hasn't shown a lot, but still did that well, the other has shown a lot and has many grand champion wins in both registries (and thanks to Larry Parnell, is driving this season, too). See our stallions here:
Stallions of Whinny For Me Farm
But, for geldings, I actually prefer B's or at least 32"+ A's. The size makes them a little more versatile and I love the looks. That said... I own just one B size gelding and the other four are A size. See our geldings here:
Geldings of Whinny For Me Farm
If it came down to only being able to keep ONE of my 17 beloved miniatures, I'd choose to keep my B show gelding,
Little Kings BT Bacardi Gold. He has so much heart, which I think comes from his sire, BTU.
Anyway, compared to my two riding horses, none of the minis ae "big"
And thanks to the minis, I'm not sure it's actually fair to still call my riding horses "riding" horses as I rarely do it in favor of doing the many mini things I love