Westpac is the only one of the big banks whose online share trading site scored five stars in Canstar's latest rating of the sector.Canstar assessed the performance of online brokerages in meeting the needs of casual investors, active investors and traders. Among the smaller execution-only brokers, Bell Direct, CMC Markets and Amscot scored the highest ratings.Westpac Online Investing was rated five stars in the casual and active investor categories, and four stars in the trader category.The market leader, Commonwealth Bank's CommSec service, was rated four stars for casual and active investors, and three stars for traders.National Australia Bank has made a big push into the online broking market since relaunching its nabtrade service in 2012. It was rated four stars for casual and active investors, and three stars for traders.ANZ's E*Trade was rated three stars for casual investors, and four stars for active investors and traders.Canstar rated the sites on price, the level of services and client support, availability of company and market information and research tools, and the functionality of the trading platform. It said two significant trends in the market were falling prices and the development of mobile trading.Since 2010 the average brokerage rate for a A$10,000 trade has fallen 23.2 per cent - from $25.75 to $19.77.Canstar said 45 per cent of people investing online were now using a mobile device for transactions and a further 14 per cent said they would be looking for a mobile platform in the near future.