As bernorange says, both have a full 1oz of gold, the eagles have an additional 3% silver and 5% copper. So the eagles are actually heavier than buffalos.
You have to be a little more careful with the buffalos, they ding pretty easily and should keep them in individual containers, where the eagles you can stack in tubes.
Both are super liquid, up till about a year ago, buffalos actually had a bit of a premium over the eagles when buying, but that seems to have evened out.
If you live in the US, which i'm sure most of us do, there is no issues with either when time to sell.
If you live somewhere else, lots of countries have taxes on 22k gold vs 24k - so eagles may not be the best choice if you are going to sell in England for example.
There are tax advantages in the US for the eagles and buffalos. Mainly, if you sell over 25oz of coins, there is no requirement for the coin shop to fill out a 1099 on the transaction. However, if you had 25 1oz Canadian maple leafs for example, the IRS would know and you would have capital gains tax stuff to deal with.
EDIT: i guess i should add, if you sell the 25 eagles/buffalos you still have a capital gains tax event, you are just left on your own to fill out all the paperwork on the honor system.