Before you start, the debate is still ongoing, some points may be stronger than others. I shall leave it to you, the reader to decide and to be convinced. For me, I use Olympus EPL-3 for travel and street. Have fun and enjoy shooting! =)
1)Battery life on mirrorless cameras is notoriously awful. For every 1,000 shots a standard DSLR can manage, Kai from DigitalRev estimates that the the Panasonic DMC-GH4 can take 500 shots, while the Sony A7R2 and Olympus OM-D series offer around 300 shots.
2)The autofocus sucks. The video doesn’t go into much detail on this subject, but DSLRs use their mirrors to create phase detection—dividing light into pairs of images and comparing them. Mirrorless cameras use what’s called contrast detection, which measures the contrast between pixels. This process is slower, worse at finding movement and weaker in low light
3)Image quality breaks down at ISO 3200. The DigitalRev team doesn’t go into much detail about this, and in fact the Sony A7R2 is known for being a strong contender in this department, but the majority of mirrorless camera still suffer from low-light noise and focus issues.
4)The size difference isn’t as significant as you might think. Put a hefty lens on any camera, and you’re going to feel the weight. The cameras themselves, too, are getting bigger than they were when the first models were released.
5)Lens choices are more limited than you think. Sure, you think the selection is huge, but budgets ultimately wind up limiting what you can afford.
6)Electronic viewfinders are problematic. For one thing, you can’t see through them when the camera’s off but keeping them on saps the battery. Optical viewfinders are also known to be clearer and offer a stronger dynamic range.