I would say, that both of these formats have their own advantages.
Parquet might be better if you have highly nested data, because it stores its elements as a tree like Google Dremel does (See here).
Apache ORC might be better if your file-structure is flattened.
And as far as I know parquet does not support Indexes yet. ORC comes with a light weight Index and since Hive 0.14 an additional Bloom Filter which might be helpful the better query response time especially when it comes to sum operations.
The Parquet default compression is SNAPPY. Are Table A – B – C and D holding the same Dataset? If yes it looks like there is something shady about it, when it only compresses to 1.9 GB