How can you look up the different kinds of mdma ecstasy pills and tell which are the best?

You can't it's impossible many people add food colouring powder to pills to make them a certain colour so you can't tell by colour the only way you can tell is by getting an ecstasy testing kit off the internet or by sending off the pill anonymously to an ecstasy testing research centre. I know that the website www.erowid.org is synonymously linked with an ecstasy testing centre.