isn't "Wahhabist" one of those things no one actually calls themselves?
Trouble is there isn't really a better way to describe them without being too broad (e.g. Salafi would include MB itself) including what they call themselves.
Whichever one is less religious?
They both are very religious, given they are religious organizations. The difference is that the former strive towards purity, respect for leaders and idealised vision of the past,while the latter are normally very politically charged, have a lot of rhetoric that borrows from previous social activist movements in mena etc. The former is more of a subculture that works in tandem with the state, the latter are populists who promise to create a popular Islamic state through democratic (of sorts) means.