Typically, Amazon's Prime Day sale tends to offer a wider range of discounts compared to its Mid-Year Sale. However, if you spot a great deal during the Mid-Year Sale, it might be wise to pounce on it as it may not come around again on Prime Day.
Another big difference between the two is that Prime Day deals are exclusively for Prime subscribers, while Amazon’s Mid-Year Sale is available to everyone. So if you aren't a Prime member, there's no point waiting. Of course, you could always sign up to Amazon Prime for a free 30-day trial if you're a first-time subscriber.