I've had my budgies for over a year now and they are such adorable little beings!
Good: They are easy to take care of, as their poop dries up quickly, so it's easy to wipe away. Their seed mess is not so bad if you put the food at the bottom of the cage and have a seed catcher of some sort. They don't cost a lot to keep and they don't go through toys like bigger birds do. What drew me to them is their beautiful colors and playfulness. I love their constant chatter, which I am able to tune out while watching TV. Although, we are going to get a stand with wheels so that we can move the birds out of the family room at night if we want to watch a movie. They do not scream nearly as loud as other larger birds, although their flock call is pretty loud, they don't do that all day.
What drew me to these little birds is that they don't necessarily REQUIRE as much attention as the larger birds. We almost got a Quaker and I am SO glad we didn't. I did not want a bird that would bond with potentially one family member and be jealous of others. I didn't want a bird that would NEED me for attention and that would act out like a human toddler. I didn't want a bird that could do serious damage with a bite. My budgies tried biting me at first, but I did not react at all and they have stopped trying to bite me since. Their bite was a hard pinch, but nothing that drew blood or was too painful to withstand.
Budgies require a LOT of patience, so if you have the patience, then they can be friendly and fun to interact with, but still be independent. These guys do not destroy anything in my house. They don't get messy poops everywhere. I can let them out of the cage and they will just hang out on the play gym and in the bird safe tropical trees that I have around the cage. They fly laps and go back to the trees. I can hand feed them in the cage and they will jump all over my hands. They will also sit on the play gym perch for training. I have started clicker training them to step up, shake hands and then I want to teach them to fly to me. They will sit on my finger and listen to me talk, but will no longer sit on my shoulder since their wings grew back. They came with clipped wings but I have not and will not clip them again.
They have just as much personality as any other larger bird and if you are home most of the day, you will have a very interactive little bird. Especially if you don't have any predator pets in your home, so the budgie can rule the house. On the other hand, it seems like a lot of people have an aviary or large flight cage with a flock of budgies that are not tame, and just enjoy watching them. The budgie will be happy in a flock, a bonded pair or bonded to a human that has a significant amount of time for the bird.
As far as talking, I read that an English Budgie holds the world record for the largest vocabulary of any parrot! They do have the potential to mimic, although it seems like teaching them to talk is more hit or miss and may require a lot more effort than larger species.
Bad: Budgies require a LOT of patience to get them to be social with humans. They are inexpensive and I fear that a lot of people buy them on impulse without knowing how to care for them or what size cage they really need for all their energy. The more time you have to devote to these little guys, the more you will get out of them. I have never owned anything other than a cockatiel (when I was a child) so I don't know for sure, but it seems like larger birds need a lot of interaction as well.
They do constantly chatter, which I like, but some people may not. Budgies tend to be flighty and the less you work with them, the more flighty they will be. Mine are getting to be more trusting, but they are still fearful of new toys, which I must place on the outside of the cage for about a week before it can go in the cage. It then takes them a day to go over to the new toy, sometimes more. This is just my birds' personalities though... Some budgies are much more outgoing and brave.
My budgies were fed only seeds when I got them, so it is difficult to get them on a healthy diet. I see that many others are having the same experience. I have been slowly and I mean SLOWLY getting them to eat vegetables and pellets. They will now eat some pellets from a dish, but vegetables will only be taken from my hand. I have had to sit with them for a very long time offering the food to them while they sit on their perch and take the TINIEST little bites of the new vegetable, so tiny that you can barely see that they took a bite. I have to eat the vegetable in front of them to prove that it won't kill them... This is a lot of work, but I really want my budgies to have a good diet, so I keep trying. I would advise finding a breeder who has already introduced the babies to vegetables and pellets so that it will be easier to feed your bird healthy foods.
Ugly: Just like most other people, I cannot think of anything outright ugly about keeping budgies as pets. They are beautiful, energetic and have a lot more personality and potential than many people give them credit for.