Tbh, porcelain is porcelain. The gubbings inside the cistern can be completely changed from as little as £30 ( fluid master replacement kit inc flush / button / fill valve ) so I'd just buy the shape / style you want / can afford.
My only advice is to make sure you get stainless through bolts, to connect the cistern to the pan, and likewise with the seat hinges.
I cant really say I've seen a cheap / bad bog before, but plenty where they've been supplied with cheap / disgracefully bad gubbings which have come with perfectly acceptable chinaware.
Any links ?