I know it's odd to think about this from an *ehem* "logical" perspective, but I'd rather be a Quincy than anything. My reasoning is mainly by process of elimination:
Human: Generally unlikely to have powers and uninteresting.
Soul Reaper: Must be dead first. Part of a large military installation that is constantly at war with tremendous monsters. Most are relatively weak as well, so it's unlikely that I'd be someone powerful.
Substitute Soul Reaper: At the beck and call of Soul Reapers who don't trust you, often with difficult to control powers. Duties often more dangerous than average Soul Reapers.
Fullbringer - Widely varied abilities and power levels, so a lot of uncertainty with them. Fun characters, probably my second choice.
Bount - Getting hunted by Soul Reapers and generally despising anyone who doesn't suck people dry is a deal breaker, despite the awesome powers.
Quincy: Still alive. A pure blood Quincy is powerful in most circumstances with access to a litany of abilities we've only started to see. The incest thing is a problem, but it could be worse.
Hollow: Have to be dead. Struggle to survive in a massively unforgiving environment where other Hollows are trying to kill and eat you. If you're lucky and powerful enough to survive that, you'll likely find yourself the victim of a Soul Reaper. Sadly, you're likely still pretty weak.
Arrancar: Have to be dead. The struggle required to get to this point is immense, but you are pretty powerful with amazing abilities. But now, you're stuck in a constant cycle of battles with Soul Society, a group that views you as nothing but a more powerful version of your faceless, insatiable bretheren. Acceptance is a long, unlikely, and dangerous road, and victory is nearly impossible.
Visored - I know it sounds awesome, but the practical realities are anything but. You have to be the victim of an incredibly traumatic event that gave birth to your inner Hollow. That Hollow is like a voice inside your head, hating you and trying constantly to grab control of your body. Sure, you can fight it for control, but you risk losing everything in the process.
Zanpakuto - Part of the problem here is that we really don't understand them yet. They grow and evolve with their Shinigami and have an as yet unknown but likely complex relationship with them. Some are constantly bruised and battered without ever being heard, like Zaraki's (yeah, he heard it recently, but after how long?) and most are in the possession of Shinigami who can hardly achieve Shikai, let alone Bankai. Most blades must feel highly discontent, but they can't do anything about it because they're linked to a single person. If that person's a failure, too bad.
Soul Reapers die a lot, so do bounts and hollows and quincies. Arrancars are murderers... I wouldn't want to be a zanpakuto... I'll be a human and stay out of that mess, though quincies are intriguing, and I like archery(not good at it, just like it)