I coded a module to pull the Mt Gox ticker data into my shopping cart software to convert the product prices from USD to BTC dynamically. My question is, what is the best data to use for this conversion? The API offers high, low, vol, avg, vwap, last, buy and sell. I'm currently using last.
Is this the best data to use for this purpose?
Well what is the "best data" from your perspective might be different from your customer's perspective.
Here's an excerpt from a related conversation:
A low margin service would be forced to set prices based on the last price on a large exchange (but also take into account "slippage" for larger transactions.)
A higher margin service could get away with once a day adjustments based on previous day's average, or something like that. Sometimes it will be in the merchant's favor, other times in the customer's favor -- but generally will even out, roughly.