Hollows are creatures from Bleach who were born from human souls, much like those who reside in the Soul Society are, but for whatever reason, they linger in the human world for longer than they should. They are thus corrupted, driven to consume the souls of both living and deceased souls. Their hunger is what defines them.
Being a hollow doesn't seem like a glamorous life to some. You're hunted by your kind and shinigami alike and treated like a monster. In many ways, that's precisely what you are. Hollows are rarely sympathetic beings, in many cases, they were as bad as a human as they are now.
10 Great: Greater Strength
As a hollow you'll gain greater strength than you ever had as a human. You'll be able to do things you never thought possible, bringing with you a presence that would make any human tremble. This is very tempting for more than just the wicked of the world, but the downtrodden as well. As a kid being picked on mercilessly by bullies, wouldn't you want the chance to one day return the favor to them? The same could go for someone in an abusive relationship. Unfortunately, that power comes with clear drawbacks, ones that you'll be incapable of overcoming.
9 Sucks: Insatiable Hunger
This is unavoidable for all hollows, their need to feed on souls cannot be controlled, and eventually it will turn them loose on the first human they see. Worse than that, often, their first target is the one that they have the strongest feelings for, such as Sora with Orihime. Your chain to this world must be the first thing that breaks before you can truly become hollow. Once it has, that lust fills your entire being, making you no better than a murderer. If you happened to be one already, the hollowfication only makes you more dangerous, as the eviler you are, the higher chance you have of retaining your intellect.
8 Great: Free To Do What You Want
As a hollow, you no longer have any rules to follow, living in a chaotic world filled with freedom, one where anarchy reigns supreme. If you wish to terrorize the human world, you are free to do so as there are no laws in place to stop you. Admittedly, you'll eventually need to deal with a shinigami, but that is a fact of life. There is always going to be a bigger fish.
While in Hueco Mundo you have equal freedom, and are able to explore the vast wasteland as you desire, be it in a group with other hollows or by yourself. The choice is truly yours, a fact that is no doubt appetizing to some.
7 Sucks: Living In Hueco Mundo
Provided you aren't still residing in the human world, a proposition that would only cause your eventual death at the hands of a shinigami, you'll be forced to live in Hueco Mundo. This is a desolate place, filled with white sand as far as the eye can see. It's not the type of place anyone would want to live. There's nothing to do, nowhere to go, and most of all, you always have to watch your back, doing everything you can to avoid becoming another stronger hollows food. That is the essential life of a hollow, one of hunger and fear.
6 Great: Upward Mobility
As a hollow, you have a great chance of upward mobility in your society, more so than even the human world. In the human world, you can continually be passed up for the promotion you deserve or jobs your more qualified for, simply because your boss doesn't like you. That isn't the case with hollows, as the only thing stopping you from moving upward is yourself. If you want to grow stronger, all you need to do is hunt your own, consuming as many souls as you can. At the very least, you'd be able to achieve Menos Grande status, if not higher. Your opportunities are limitless, as only one thing matters to a hollow, strength.
5 Sucks: Appearance
Looking like a giant nightmarish creature shouldn't be on the top of anybody's wish list, even some of the most cold-hearted killers in the world wish to remain human. As a hollow, that is entirely out the window, as you're forced into wearing the grotesque skull mask.
Not only that, but that mask will also be the remains of your heart, becoming the source of your powers going forward. Appearance aside, we can only imagine how awful the transformation process is, forcibly having your heart removed sounds far from a pleasant experience.
4 Great: No Society
This could be positive or negative, depending on how you look at it. On one hand, society helps keep the structure in the world, making sure it doesn't fall into complete chaos. On the other hand, it can suffocate you with rules to follow, stripping you of your freedoms bit by bit. Even Aizen understood this, being understanding when lower-level Espada went against his direct orders. Hollows aren't a type of creature that wants to be governed, nor are the people who would wish to become one. They are the types of free spirits that want to do as they wish when they wish to do it.
3 Sucks: Having No Heart
This was touched on briefly above, but it deserves its own mention. The inability to feel emotion sounds awful and is a fate no person should be forced to go through. We all need to be able to feel, even heartbreaks and painful memories. They are all there to help the moments of joy feel that much greater, as without that, we are empty. This is explored with two members of Espada, both Starrk and Ulquiorra desperately trying to understand humanity in their own ways. While their heart may be the source of their power, is it worth the lack of feeling?
2 Great: Able To Regenerate
A greater strength was touched on, but not some of the powers they can gain from that strength. One that even lower level hollows have is the ability to regenerate. This comes in handy when you're stuck in a world where you could be someone else's meal at any moment. It's what helps many gain strength as well, giving them the ability to recoup from battles at a faster rate. Surprisingly, so many of the Espada chose to give this talent up in favor of more raw power, especially when you consider Ulquiorra's ranking.
1 Sucks: Transformation Process
This is a culmination of a few items on this list, and the largest reason why being a hollow would suck. We've touched on the act of losing your heart and how that becomes your mask already. The true horror lies in the process before that. As you change, you're chained to an area, trapped in between being hollow and being a spirit. You are what's known as a Jibakurei or demi-hollow, a being forced to remain in the same spot for months at a time until the process of becoming a hollow is over. That's an excessively long time to undergo what is no doubt an immense amount of pain.