Although they contain the most amount of cards, the vast majority of them will be common or uncommon, as there are only one or two rare or mythic rares in each pack
Current definition Reserved cards are cards that will never be printed again in a functionally identical form
Some examples: Swords to Plowshares, Teferis Protection, Chaos Warp, Great Train Heist (or other Spree cards, you pay extra costs but can go wild), Akromas Will, Deflecting Swat, Wear/Tear, and my personal favorite, Reprieve
There are some commanders out there that can be a huge help with getting your dragons out nice and early so you can hit some faces
An example of this would be a goblin deck
Sadly, its looking tricky to buy online, and while packs and boxes are rarer than hens teeth right now, theres a good chance that problem will ease off once more product becomes available