Well certainly the most absorbable/best Vit C is food based, meaning it has all the factors your body expects when it encounters ascorbic acid/ascorbate therefore being more beneficial. That said, it can get quite pricey to take food based vit C supplements at some of the suggested levels (few grams), or ingest lots of vit C fruits and vegetables.
On a balanced diet and healthy body you might only need a few hundred milligrams; but since we are bombarded with toxins every day typically is a good idea to boost that antioxidant to help out on detoxification, specially if toxins have accumulated. It is important to keep in mind on the form of Vit C as you said it may do more harm than good.
Personally I have been taking a food based Vit C with bio "flava flave-noids", and use a couple packets of emergen-c (has 7 different mineral ascorbates) a day for a total of ~3grams a day.
Mike