I'm a legacy airline, wide-body FO that lives in base and sits in the bottom 10% of my seat. As someone else mentioned, it can be a great part-time gig if you live in base. My normal month holding a line is 9-12 days of work with 6-10 nights gone. When I bid reserve (usually in the winter), I generally go to work 0 to 9 days a month, while sitting reserve from my house. Day 1, I usually leave my house between 1200-1900 and on the last day I'm usually home between 1330-1700. Some months I drop my schedule down to 6-9 days and some months I pick up an overtime trip. That flexibility is what makes this job so awesome to me. Thanks to an overtime trip this month (15 days worked), I plan to drop my July schedule down to 6 days and enjoy a nice long vacation (including July 4th off) without actually taking any vacation. I'll take a pay hit this month, but the overtime trip from last month more than makes up for it.
Conversely, at my previous airline, I had a 2-leg commute to sit short call reserve 18 days/month. It SUCKED big time. Don't commute (I know, easier said than done for some)! As others have said, it can vary wildly based on when/where you were hired and dumb luck. Best ways to help yourself is to do what you need to get hired ASAP and live in base. Once there, get senior and stay senior or get on a WB ASAP. I can't remember if I said it, but don't commute.