In general what grarpamp said is true, however we should remember that I2P (aka Invisible Internet Protocol) is designed to be "a real undernet" and thus it is focused mostly on hidden services and invisible hosting. It results in fact that there is much less outproxies than in TOR network. Using I2P to acces a "standard" Internet but in anonymous way is much less efficient than via TOR only because of that design issue, moreover I2P is just less popular than TOR and has less participating nodes, what additionally decreases it's efficiency.