do you get the bid and offer prices?
That would be closest to reality IMO
I don't know that the bid and offer prices are closer to reality than the real transaction prices. In some cases the highest bid/offer price would be a few cents off the transaction figure. By the same token in a choppy market the bid and offer could be quite substantial. The fundamentals of the exchange are that at a point the bidder and offeror agree a price at which they are prepared to buy/sell and the transaction is concluded. So my view is that we need to stick with the last transaction price
Last transaction price is always the reported price. The bid (for sellers) and offer (for buyers) is the realistic transaction price at any point in time. However, with many electronic systems there is often very little volume on the leading bid and / or offer. The price you end up trading at (assuming a best price order) would be the weighted average of the price and volume available. One really needs to see the "stack" i.e. list of all bids and offers and the associated volumes to see where traders are actually interested in trading at.
Often in fast markets you will see electronic systems picking off the bid and offer in small amounts, trying to lead volume into the trade. However, volume can often be hidden as part of an "iceberg" order e.g. you think you are hitting the bid in 1,000 lots and driving the price down but the bid keeps coming back at the same price because the trader has placed an iceberg for 10,000 lots. These are where the real games are played in trading.