choiahn wrote:
Please advice which one is better for landscape and family photo for Canon 80D body?
They will be about equal for those purposes.
The USM is a new lens (2016) and usually is what's bundled in kit with the 80D, was introduced this year alongside that camera.
The USM and STM (2012) versions appear to be the same optically and in most specifications: same number of elements and groups, block diagrams appear identical, aperture blade count, close focusing distance and max magnification are all identical. The primary difference is the speed of the autofocus drive. The USM lens is 2X to 4X faster, according to Canon themselves, so would be a better choice for sports or other action photography and for shooting moving subjects.
The USM on that lens is a new type that Canon calls "Nano USM". In the past, USM lenses weren't ideal for videography. STM lenses were recommended instead (quieter and smoother), while older USM lenses were preferred for their speedier performance, but were too noisy and not smooth enough for videos. However, the 18-135mm USM's focus drive is optimized in both respects. Since the there are new EF 24-105L and EF 70-300mm lenses also using "Nano USM". Presumably those are also both good for both fast action stills and videography, same as the 18-135mm USM.
Also, Canon introduced a power zoom module especially for the new 18-135mm. This is another thing that videographers might like. But it's only usable on this one lens, as of now. It won't fit and work on any other Canon lens or even the earlier, non-USM versions of the 18-135mm.
So, if you need the speed of USM, the new lens would be a better choice. But if STM is adequately fast (it's faster than micro motor), that lens is slightly less expensive. There's only about $50 or $100 difference between the MSRP, but the STM lens has been available for a while and it's street price has settled a bit, making for a bigger difference in the price. Plus the STM can be widely found used or refurbished, for additional savings. The USM lens is simply so new that it's still bringing full MSRP and can't be found used or refurbished.
Note: There also is an earlier (2009) "micro motor" version of the 18-135mm, usually selling for about $50 less than the STM version. The easiest way to distinguish it from the others... it simply isn't marked either STM or USM. The micro motor is the slowest, noisiest and least smooth of the focus drives.
Personally, for landscape photography I'd often want a wider lens. Among ultrawides, the Canon EF-S 10-18mm IS STM is one heck of a bargain at under $300. Most lenses of this type cost at least $200 more. It's also the most compact lens in the category and the only one with image stabilization. It uses 67mm filters, where most ultrawides use 77mm and a few 82mm. The 10-18mm is a bit plasticky, but for such a bargain price I suppose that's to be expected. Various reviewers have raved about it's image quality, some say it's as good or better than the older Canon EF-S 10-22mm, which costs more than twice as much and has long been considered one of the best ultrawides from anyone. The difference between STM and USM wouldn't bevery noticeable on an ultrawide... the focus drive only needs to move the AF group a smidgen to focus such a wide lens. STM vs USM is a bigger concern with telephotos, macro, etc.
And for portraiture, especially indoors by available light, I'd be inclined to use a faster prime lens such as a 50mm. The bargain lens in this category is the Canon EF 50/1.8 STM, almost 1/3 the price of the more upgrade EF 50/1.4 USM (which is what I use), both of which are far less expensive than the premium EF 50/1.2L. There is a now-discontinued micro motor version of the EF 50/1.8, too... but I'd highly recommend either the STM version or the 50/1.4 USM over the micro motor. The micro motor lens' autofocus is noisy, slow, and sometimes even a bit erratic. The STM version is the same price, too.
For wider group shots indoors by available light, on an APS-C camera such as 80D, I'd use my Canon EF 28/1.8 USM. It's a nice "standard" lens on crop sensor cameras... compact, fast focusing, mid-grade build, and with a nice, big aperture if needed. The only thing is that a wider lens such as this tends to exaggerate perspective, so has to be used carefully for any sort of portraiture.