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.

[1] https://en.wikipedia.org/wiki/Decay_chain#/media/File:Decay_...

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.