The SL1's JPEGs look clean up through ISO 800, but there's a big jump in softness between ISO 800 and ISO 1600. I thought that the fuzziness at ISO 100 and ISO 200 was camera shake caused by the mirror slap at shutter speeds below around 1/100 sec, but looking back at my T5i samples it's there at lower ISO sensitivities, too. It could be that the bouncy mirror affects both cameras, but at least the SL1 has a soft shutter mode that seems to improve things.
Noise and JPEG processing, high ISO sensitivities
I wouldn't recommend shooting JPEGs above ISO 1600 with the SL1 unless you'll be using them at small sizes.
ISO 100 JPEG
The kit lens and default Picture Style settings result in sharp but not oversharpened images. You can get better results on those high-contrast edges (like the pink on green) by processing raw, though.
(1/100 sec., f19, ISO 100, AWB, evaluative metering, 18-55mm STM lens at 51mm)
ISO 400 JPEG
ISO 400 is the top sensitivity where you can get clean JPEGs. They're very good.
As usual, Canon's default Auto Picture Style as well as Standard deliver brighter, juicier colors than nature intended. Neutral is only slightly toned down a bit -- just a hair less saturated and with no sharpening applied -- but not as accurate as it used to be. Faithful is flatter (lower contrast) with no sharpening.
(1/100 sec., f5, ISO 100, AWB, spot metering, 18-55mm STM lens at 18mm)