So as another example I just had a size 1000 WC go through the autoexchange setup at trademybit and it traded through at -20% to where the market was just before and just after the exchange from WC to BTC as done through the automated exchange setup at TMB. Per coin value was .00000850btc as obtained by TMB's autoexchange, but the market for this coin was much higher just prior and just after this trade went through. Perhaps the markets are super thin and the exchange crashes it, but this is a major affect on coin profitability if I mine when the coin is valued at xbtc/mh's, but the exchange system consistently gets 10-20% below the going market rate before and after the exchanges to btc are being made.
Edit: A following trade of WC as done by the autoexchange at TMB got much closer to the market rate, though here the trade was for a lot less WC.
I know I can manually do the exchange, but i'd like to see these exchange rates got for our mined coins not be consistently and in some cases substantially lower than where the market trades at just prior and just after the trade goes trough, or if this is unavoidable due to thin markets then have the value for mining the coin adjusted in some manner.
Actually I was manually trading WC and I sold for it's highest value on first day. Days before I switched autoexchange off, because I wanted to trade by myself on fresh coin. I switched autoechange off when price was 0.00000560. I sold/bought until it reached 0.00002000. Later I sold it in blocks at almost highest price that day. Later I was again buying/selling until it fell to 0.00001380. It was huge profit.
As I was trading, pools had some troubles in selling big walls (especially after first down). After each trade I looked into TMB to compare. I was very surprissed how good TMB is trading. For the most users it is important to get their coins exchanged fast. That was the case. TMB traded on cryptsy, where I did too. Difference was maginal: (I cold 0.00001598, TMB: 0.00001502). Difference is 6%. There were also couple of trades where TMB made 20% more than me, just because I went too late with the price down.
My advice:
If you are looking into profit, change to manual exchange (off course only if you know what you are doing). If you do not know what you are doing, pay out to crypsty and sell for highest price. Sometimes you will wait longer for trades but at the end you can see difference.
In my eyes TMB trades very well.