This list is non-exhaustive.
1099:
Your customers will send you a 1099-MISC form each year stating how much they paid you. It's solely up to you to pay any applicable income taxes.
You'll pay for your own healthcare and retirement benefits, and anything else an employer would typically pay for.
You won't get paid vacation or sick days. If you're being paid strictly on the basis of hours worked then you won't get paid when you take time off.
You'll have more freedom in choosing what kind of work you want to do and what kind you don't want to do.
You'll have more freedom to set your own hours and schedule.
You'll have more freedom in choosing who you will and won't work with.
You'll be free of almost all company politics. As a 1099'er myself I don't know, care, or get involved in the internal company politics of my customers.
Your customer should reimburse your travel expenses and you should bill for your travel time and mileage. While you're traveling for work on your clients behalf you can't be performing work for, and earning money from, other clients. Your customer should pay for that time and for those expenses. I bill for travel time and I expense my mileage. You can and should do both if you're using your own vehicle. Contrary to popular belief, it's not one or the other, it's both. Your travel time is billable just as it would be when you're performing actual work. Your mileage is an expense that should be reimbursed.
There are many online calculators, articles, etc. to help you determine how much your billable rate should be, but it should account for the costs that the employer is no longer paying and that have shifted to you. My hourly rate is about 33% higher than I'd typically earn as a salaried employee.
