Depends what you want to be able to do, as a first donation I suggest Multihome, Water, or TP as they are some of the cheaper ones, if you want to spend more cash go for Ext Cmds, or fly.
Multihome is by far the most convenient donation feature that everyone usually donates for first. It's one of the cheaper features and it will make your life a thousand times easier
Eh, the way I was set up until I got multihome was a homeset at a farm, and then I used a town with a portal, if the farm has a portal even better, then you can use the home for a personal use. I would get fly first, if multihome makes your life 1000 times easier, fly makes it 10000 times easier.
I can see the points of the other users. It really depends on how you earn money or how you spend your time on ECC. My first donation feature was TP. A simple $20 feature which was extremely efficient for trading with other users or selling services. It also came in handy with my town that didn't quite have a portal. But again, it depends on what you do when you're on the server.
I really appreciate your points! I have recently payed for access to a nice farm complex so teleportation may bode me well. If a sale comes, donating for flight permissions may be an option, but for now I'm not sure.
Wait for a sale, and get Teleport, Multihome, and Water as your first 3 donations. They total $50, but are well worth it.
Easily mulithome and tp are best for newer players. They were my first features and I use them very often. They will always help you.
Multihome is a great donation. But if your house and farm both have portals I would suggest fly. If they do not then get multi home and teleport.