The cheapest way is to send your money from your bank account directly to your bitcoin wallet created in bitkonan site or localbitcoins but I prefer bitkonan because they look faster for me with very low fees.In bitkonan you can also buy/sell crpytocurrencies to make a money but you can also save your earnings so that means that it can be your bitcoin wallet and there is not neccesary to have other bitcoin wallet ,only if some invesment site want from you to use some kind of bitcoin wallet then you must use more wallets and then 1 bitcoin wallet isnt enought.I dont know any other kind of deposit which we can make faster.Only I know that xapo offer a deposit with credit card but I dont know how much time it need to pass to get a deposit directly in own bitcoin wallet.
yes i have a friend there in USA and often we talk about bitcoin, once i asked from his about the way he buy bitcoin and he also told me that he is using bitkonan. according to him it is one of the fastest and reliable way of buying bitcoin with a very very low fee. he also told me about some other good feathers of bitkonan i am not remembering correctly.