Buys on BitFunder are free - fees are only incurred when selling.
BTCT charges 0.2-0.25% for a buy and 0.2-0.25% for a sell, so a buy and sell would add up to 0.4-0.5%.
BTCT also charges fees for BTC withdrawal while BitFunder does not.

BitFunder also requires that any BTC in/out go through an extra layer service called WeExchange while BTCT allows direct deposit/withdrawal of BTC. Some argue that the WeExchange service is an extra hassle, while some say it provides an extra layer of protection (if your BitFunder account is hacked then the only way for BTC to get withdrawn is through WeExchange).