In my completely biased opinion, I say the SL2. I say biased because it was my first camera as well and I have no knowledge on the D5300.
Things I can tell you from personal experience with the SL2 are as follows:
- It was smaller than I expected it to be. I had been using a friend's SL1 before and was excited when I found out the SL2 was coming out right as I was getting ready to purchase my own. It was noticeably smaller than the SL1
- The LCD screen is very nice, works great for odd angles to be able to adjust it. Touch screen adds a little extra value, however I rarely use the touch screen feature.
- It has condensed the Shooting Mode wheel quite a bit, which is clean but took me a minute to adjust to. Instead of having a specific Portrait, Landscape, Sport (and so on) mode, it has a Scene mode and inside that you select which of those you want to use. All of those features are still there, but they added a step to get to them. Again, kind of good, but not what I was used to from other cameras.
- It uses the EF mount, so you can use about any Canon lens on it
- When using Continuous shooting, if shooting in Raw or a Large file format, you only get 5 shots before it has to load up new shots. So you can get 5 quick bursts, but then it will take about 5 seconds before you can get a 6th shot off, and so on. This has been my least favorite part of the camera as it sucks having to wait after 5 shots every now and again. The only fix I was able to find is lowering the file format, but I don't want to do that so I just try to avoid situations that need that.
- It has WiFi connectivity and all that new jazz, which again is a nice added value, however I rarely use this again. I'm sure it can be useful, but I just do what I am used to doing which does not involve WiFi, touch screen, etc.
I hope this helps. Again, this is just from my personal experience from owning the camera. I would be glad to answer any other questions you have about the SL2 if you want to know something specific!