I agree with Daniel - Always use your ISA! It is always worth it. If I put £10,200 in shares in my ISA for the next few years for growth, then want an income from my ISA I switch to high yield bonds/gilts etc and get tax free income from an ISA pot and have benefited from growing my ISA with shares in the early years. As a basic rate taxpayer this will have been a very worthwhile exercise. Also, we don't know what tax regime we will be in in the future!
Didn't the original question revolve around which platform to use for the ISA? Oh well.