Well, I think we need to differentiate between powerful and long-lasting. Reclast may be more powerful in that it can suppress osteoclast activity with just a single dose that lasts at least a year and maybe up to 3 years while it takes weekly repeated doses of alendronate taken over years to achieve the same osteoclast suppression.

However, alendronate has a half-life of 10 years because it is taken up by bone and is only released when bone breaks down again. If you come off alendronate, osteoclast activity will resume and when the bone breaks down, the drug is released into your blood and is taken back up by the bone. This means that its effect lasts longer than Reclast. This is also one of the reasons that it's recommended that anabolics be used first before bisphosphonates because a bisphosphonate like Fosamax can blunt their effect. Unfortunately, this is the situation that I am in since I was on it for so long and am now on Evenity.

Edited to add after doing more research that Reclast also binds to bone surfaces and exhibits the same effect as alendronate with regards to being released and taken up again by bone. So it looks like both have lengthy durations of effect in that regard but yes, Reclast is more powerful being that it only requires one dose.