lens - What are the advantages and disdvantages of the Canon 18-55 IS MKII vs IS STM kit lenses?

I'm trying to figure out the difference between the IS MKII lens and the IS STM lens.

Specifically, I am looking at the Canon EF-S 18-55mm f/3.5-5.6 lens. On that Amazon page, there are three options; of the EF-S, one is listed as IS MK II; the other is IS STM.

I'm still not sure which is best to purchase - given the comparable price - I have heard pros and cons of each.

I understand that STM is a newer lens technology w/ a stepper motor for focusing, if I understand correctly, on manual focus, rather than adjusting the focus directly, you adjust the focus ring, and the stepper motor brings the lens to that focus point.

I have read that STM can be slower to focus than USM - however, I don't think the MK II has USM. The STM is supposed to be quieter, and thus better for AF while filming video.

Since the STM lens is newer (I think), is there any reason to buy the MK II? (The MK II is actually more expensive on the page listed.) Are there benefits to it, or pitfalls to the STM that I should consider?

Side note; my camera is an older Rebel XS; I'm not sure if the STM will work fully with it.

Answer

According to the Wikipedia article comparing all Canon EF-S 18-55mm version the STM version has (in addition to the new STM motor) a new optical design (13 elements in 11 groups vs. 11 elements in 9 groups), internal focusing and an extra diaphragm blade (7 vs. 6)

So, the EF-S 18-55mm IS STM is not just the EF-S 18-55mm IS II with the new motor but a completely new lens that seams to be slightly better than the old design in every way.

Even if you don't need the advantage of the STM motor for video I see no reason to buy the older version (unless it's cheaper), I also don't see a compelling reason to upgrade for someone that already has the IS II but the new STM version is better.

BTW, you can usually buy seconds hand kit lenses for next to nothing because a lot of people want to get rid of them when they upgrade, a quick look on eBay shows that the EF-S 18-55mm IS II has been sold for as little as $40