Wikipedia, though it can be changed, is monitored by credible people who know about the subject. If someone adds a false statement ,though it will be there for a little while and maybe a few will see it, the monitors will change it. All information on Wikipedia has links to where it came from and isn't biased. If a statement is biased once again, the monitors will reword it.
Typically, a textbook is a combination of other textbooks. Each "new" edition isn't really new at all. A textbook can tend to have basic coverage on certain subjects. The Wounded Knee Massacre ,in a typical textbook, states that someone fired a shot and then killing broke out. However, the Wikipedia article gives eyewitness accounts from both sides.
I feel Wikipedia is a pretty reliable source to get a general idea on a subject. However since at times you may be looking at an article that was edited and hasn't been reviewed yet, it may be wise to use the links they provide as a more concrete source.