This is sort of a loaded question. But I'll throw my 2 cents out there...
I've worked at just about every type of flying operation around. Flew traffic watch, skydivers, flight instructed everything from private pilots to ATPs, pictometry-type stuff, frequency testing for the FCC, and I dabbled briefly in charter and corporate aviation in King Airs, Lear, and a CJ. I've now been at a 121 regional for shy of 3 years.
The most fun I've ever had flying was frequency testing/picto stuff and flight instructing. I won't get into it but I had a great thing going with both of those jobs and in hindsight it was a lot of fun. But, they were still a "stepping stone" on the path I wanted my career to ultimately take.
Charter/Corporate aviation is okay. I think it suits some people better than it suited me. It gave me my first turbine experience and showed me how diverse aviation can be. I met some great friends that I still keep in touch with to this day. That being said, "I'm not a 'yes man'." And what I'm about to say isn't meant to imply that ALL Charter/Corporate pilots are "yes men" (or women) so bare with me. I don't want to come into the office on my days off and/or wash the airplane. I don't want to empty the lav. I don't want to throw bags. I don't want to have to feel like I have to suck up to the boss so I can hopefully sit in the left seat one day if the guy over there decides to quit or retires. I don't want to tell the customer they can't bring their 3 extra friends and their 20 extra bags. I had no problem doing it at the time. But it's just not what I want to be doing long-term. Of course not every outfit is like that and the times have certainly changed a bit, but that was my experience. It just wasn't for me.
I've been at PSA now for the better part of 3 years. I have to commute to work up in CLT instead of driving 10 minutes to the airport, but that's okay with me because this job (for what it is) is leaps and bounds better than any other (jet) job I've ever had. I didn't sit much reserve here, and I held a line in my base of choice within 6 months. Fast forward a couple years and I'm a senior FO who has been bypassing upgrade for several months (for reasons that are my own) although that is going to change here pretty soon. This year I have not been off less than 15 days in a month save for 1 month I decided I was going to make some extra coin and I was off 13 days. Most months I'm off 17-19 days thanks to our SAP (schedule adjustment period) and I credit anywhere from 65 to maybe 80 hours in an "average month". I haven't spent a single holiday away from my family and I haven't missed one single important engagement thanks to it. I'm on track to credit around $65,000 this year and I feel like I barely work. When I upgrade I will still be able to hold a line in a commutable base and take advantage of the SAP and I'll likely make about $75,000 (could make more but I don't like to work too much truthfully). Some people say living in base can't be beat, and that may be true in most cases. That being said my commute is pretty short/painless and I'm actually Home more than I would be if I lived in base because I can bid overnights in my hometown. Some months I've had 4-5 overnights here.
So in my opinion 121 is leaps and bounds and night/day better than anything else. However I've had a really great experience so far and I know it hasn't been as good to many out there. This industry is all about timing and so far I've been pretty lucky. I'll just add this little bit of advice I heard from an older pilot who was at the twilight of his career. He said that if he and the other older guys he still talked to could have gone back, most would have just stuck it out in 121 instead of pursuing 135/91 flying. He said the pilots he knew who were the happiest, healthiest, and wealthiest (cliche huh?) over the long term of their career were all airline guys. They had the most overall career earnings, better retirements, and much better career stability. To echo what others have already said to you above. Seniority really is EVERYTHING in this industry. Do not wait one class date longer than you absolutely have to. I took a 6 month break between my last job and PSA and I regret it to this day. It can be the difference between years of reserve and holding a line. The difference between years of having holidays with your family and sitting in a crash pad on reserve over Christmas. The difference between a successful marriage and a bitter divorce. It is everything.
