The two main choices you'll find from Canon are that you can get an 18-55mm f/3.5-5.6 with either the newer "STM" (stepper motor) design, or the non-STM version "II" design (which uses micro-motors).
The STM motors are significantly quieter ... but they are also faster to focus. So even if you aren't interested in the "quiet" feature (great for video when you use the internal microphone) ... being "faster" is generally always going to be welcome.
One feature that really sticks out in my mind ... is that the STM version now has "internal focus". On the older non-STM design (the version "II") lens rotates the front of the lens as you focus. If you have a polarizing filter on the lens, this causes the filter to rotate ... and you're always having to re-adjust the filter tuning after each focus. The "STM" version only moves elements internally ... the front element no longer rotates. This means you're not constantly having to adjust the angle of your filter.
Other than that... both lenses claim 4 stops of Image Stabilization.
Both lenses have decent optics ... with some optical flaws (chromatic aberration).
The STM version has 7 aperture blades vs. 6 on the older version "II". The number and shape of blades controls the shape of the aperture opening, more blades generally results in a more rounded opening. Two visual effects might be noticed based on aperture blade count and aperture opening shape.
- A more well-rounded aperture will tend to have a smoother quality in the out-of-focus background or foreground blur. Also any point-sources of light will tend to create a "disk" or "spot" in the shape of the aperture opening (a more rounded opening results in these spots better resembles circles instead of polygons.) This effect is mostly noticed when using a shallow depth-of-field.
- At higher f-stop values, each "point source" of light (e.g. a string of holiday lights ... or distant street-lights and other light sources in late-evening or night-time city-scape photographs) will create "diffraction spikes" that cause each point-source to resemble a spiky star. The number of diffraction spikes is based on the number of aperture blades. Each "blade" edge creates two spikes (opposed at 180°). In lenses with even numbers of blades you'll count the same number of spikes as you have aperture blades (e.g. a 6-blade aperture would have 6 spikes). In lenses with odd numbers of blades (e.g. 5, 7, 9) you see twice as many spikes as the number of blades (a 7-blade aperture creates 14 spikes). This is because the diffraction effect in physics creates TWO spikes off each edge. When you have an even number of blades (e.g. 6) you technically have 12 spikes... but they overlap as 6 "pairs". The brighter the light and the longer the exposure, the stronger the diffraction spike. This effect shows up mostly at higher f-stop values (e.g. f/11, f/16, f/22). The higher the f-stop, the stronger the effect.
The above image was captured using a lens with 8 aperture blades (you can count 8 diffraction spikes on each of the brightest stars in the image). Some dimmer stars show shorter diffraction spikes. This was capture at f/10. The effect is intensified at higher f-stop values.
For those with deeper pockets... the EF-S 17-55mm f/2.8 IS USM. It's main advantage is that it can provide the lower f/2.8 focal ratio at all focal lengths in its range. At the 55mm end... that's two full stops "faster" than the f/3.5-5.6 lenses.