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In general there is an inverse relation between the half-life and the intensity of radioactivity of an isotope. Isotopes with a long half-life decay very slowly, and so produce fewer radioactive decays per second; their intensity is less. Istopes with shorter half-lives are more intense.

In nuclear waste, isotopes with very short half-lives, say a few days or even a few weeks, are not the major concern. They will decay to negligible amounts within a year or two. Isotopes with very long half-lives, more than 1000 years, are likely to be less intense.

Long-term isotopes are more complicated. They don't dose as heavily, but there are a lot more issues than just that. Plutonium for example is comparatively long-lived, but some of its decay products can be quite nasty. At the extreme end are isotopes that are so long-lived that their hazard levels are close to zero. Uranium-238, the kind left after the fissile 235 is removed, pretty well falls into this category.

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The problem is bioaccumulation of radioactive isotopes.