Working for startups or big corporations (plus there are more options!) is different, but not as much as people put it. Each are going to have pros and cons... and sometimes the pros and cons are the same!

From my experience (that is anecdotal, as each company is a new world):

Startups: you need to deliver and deliver fast. Many times long hours and at weird times (I once had to take a client's call on a Saturday at 8pm while having dinner with some friends, and ask for my friend's computer so I could vpn to work.) You gain a lot of experience and learn a lot, which is great... but... that learning and experience is often not the best: having to deliver fast means cutting corners, and choosing speed over quality, you will learn practical skills and get technical knowledge, but it may not be the best practices. You'll get to wear many hats (and I really mean it, to the point of even having to send snail mail as a developer, or organize marketing content for conferences... and I don't mean slides, but folding brochures and picking swag from the store.) And that's good. You'll grow in all directions a little bit. Projects tend to be more interesting (not always) and there's a lot of responsibility and pressure: if you don't deliver, the company may well disappear. Start ups are great for younger people without family ties, who value more the project than the (long-term) perks or salary. If the start up succeeds (90% of startups fail), you'll hit jackpot and most likely move to the next one.

Big corporations: one bad thing about big corps is that you stop being a person to become a number, a cog in an engine whose only job is to make money. That dilutes responsibility, but less responsibility doesn't mean less pressure: you'll be working in multimillion contracts, if you don't deliver on time, the corporation may lose huge amounts (in the 6-7 figures, and good luck explaining that failure to executives). So don't think that it will be "5pm. Clock out. I'm done for the day." Salaries tend to be higher, and long-term perks tend to be sweeter (higher 401k matches, stock options, better and cheaper health insurances.) Also, let me break the bubble of work stability: yes, a big corp will not just close shop and be done as a startup, but layoffs are incredibly common (with or without economic crisis) and incredibly unfair. You may be the most productive employee in the company, but if your department is gone, you are gone. Another bubble to burst: opportunities for growth. May be educational, yes (learning may be slower but it can be of higher quality: big corps usually have learning budgets, even for grad schools), also because there are more processed and people in place, you'll be able to grow vertically (specialize) even if slower; but career-wise, it is more common to jump diagonally to a different department (or company) than to go up vertically (promotions).

Medium Enterprises (SME): They are more established and the survival pressure is gone (but still there), and normally their goals are more modest and their clients more "understanding" (no multimillion dollar contracts and the sword of Damocles of layoffs not hanging over your head continuously.) Smaller groups, maybe not as interesting projects (this depends highly on the company, I worked as a developer in a company that did smaller projects for the government and they were surprisingly challenging and interesting... and if they weren't, it didn't matter because they'd soon be over and get a new one.) The long-term perks and the salary won't be as big as the big corp, the chances of potential reward will be lower than at a startup and, in my opinion, they are more stable and balanced (both in terms of job security and work-life balance) than startups/big corp. These are the ones where I enjoyed my time the best because they offered a nice balance between startup and big corp life.

My two cents: focus on the project more than the type of company. Of course, there will be personal factors that may make you choose between small or big, but in the end, you'll be happier with a project that you enjoy and makes you happy, independently of it being in a startup, a small/medium company, or a big corporation. And that will impact your overall productivity and burnout feeling.