If you think Airtel 3G tariff plans are very costly, you will be shocked, if you look at the fine prints on the 3G usage for roaming. It costs 30 paise per 20KB, which works out to Rs 15 per MB.
If you have the 100MB for 100 Rupees plan, if you are in roaming and used 100MB, it will cost you whopping Rs1500/-
Vodafone does not have the Tariff plan during roaming mentioned in their site. We could assume they charge the same amount. In that case it will be far better than Airtel 3G.