I've done both . . . 91/135 jets and National/Major 121. I like both, but here's my take-
1) Corporate flying is more fun. Trips to more varied places, more challenges in planning and executing trips. Being contactable on days off, and difficulty getting time off for family things was something I tolerated as a younger, newer Pilot, but am not as willing to endure now.
2) The worst flying at the major airlines as a newhire or junior Pilot, most closely represents a decent corporate or 135 gig- hard days off, but no idea what to expect for the days you are assigned to fly.
3) Once you hold an actual LINE at an airline (generally takes about 10-30% off the bottom of the seniority list in your base/equipment/seat, depending on your airline's staffing method) the difference is night/day. You can trade your trips with other pilots or with the Company, trading in and out of trips until 48-72 hours before the trip starts. Once you report, you generally know every leg you will fly and where you will overnight, unless weather starts creating havoc, or something happens to force a change. On your days off, no one will call you, and if they ever do, you are not required to answer the phone, or to call them back, period.
Drawbacks- Loading canned flight plans and flying 3-4 (or more) flights a day gets pretty old for me. They also take a lot of the Captain's authority and distribute it to people who aren't even on board- Dispatcher, Ops Agent, etc. The Captain loses authority but retains responsibility. The Airline will often sacrifice a Pilot to the FAA to save themselves from a violation or penalty, and, while hopefully, the Union can get it resolved, you are definitely under closer scrutiny than a 91/135 guy whose plane doesn't snitch on him if he moves the flaps while taxiing or decides not to use Max auto-brakes on a dry runway.
So, in my humble opinion, corporate flying is more fun, and often more challenging (circling approaches at an uncontrolled field?) but I decided to trade the fun for the schedule and pay of a 121 carrier. As senior FO, I can count on 17-19 hard days off a month, so I'm willing to fly my ass off on the 13 days I'm working, and forgo the Tellurides and and Aspens until I'm on vacation or just off work.
Best of luck whatever you all decide to do.