Half-life is longer for uranium, but I would say they are just as radioactive, as they are in secular equilibrium and apart of the same decay chain [1]. They are just as "radioactive" in this configuration, as they go through the same number of decays. Their concentrations can change.
SI measures radiation in decay events per second. The rate is important because we mostly worry about decay product exposure during our lifetimes, or maybe how long a mass must be contained until it stops being an acute risk to our species, rather than the grand total of decay over astronomical time scales.
[1] https://en.wikipedia.org/wiki/Decay_chain#/media/File:Decay_...