If the other side also has no good ranged attacks the flying team more or less wins automatically. Both are clearly very powerful, if you've got two sides in a combat one of which can fly and one of which can't the flying side has a huge advantage. The Boots give a fly speed equal to your walking speed for 4 hours per day divisible into 1 minute chunks while the broom gives you a flat 50 foot fly speed all day long, decreasing to 30 feet if you are particularly heavy. Among the first I came across were the Winged Boots and the Broom of Flying.
There are a few items which give the ability to fly in the 5e DMG.
The price tables below have been compiled into an excellent pdf by Inconnunom.
