Personally started from a 135 op.
I was there for five years (but spent 1 as a FF) and the rest of the time doing jack-of-all-trades stuff for the same company on the ramp. I noticed it was a VERY family-oriented company after year 1 or so - and the airport became home from 2 to 5. (Well Burrito, why'd you leave then? I'm glad you asked, other burrito.) It's all about what you're after. The place was getting old, and I was looking for 121 experience. AND - bonus round - every airline's different. Flight following at NetJets is a WORLD of difference from flight following at, say, Cape Air. Much like 121 - Regional dispatch is a world of difference from mainline dispatch - sometimes even dimensions away. If you've got the opportunity after some interviews, ask to see the SOC/IOC/OCC/ROTC/ARALSEA or whatever that carrier is calling it. On IROP days, you may not get so lucky.
Frankly, as someone who loves this industry probably a little too much, I'd say this: any experience is better than none. ALAs know weight and balance. Fueler/de-icers know average de-icing times, holdover limitations, and fuel capacities (if they're smart). CSA/CSRs know what it's like to upgrade/downgrade aircraft on stupidly-busy routes. Crew schedulers know what it's like talking to crew members. ... I think.
May be stretching a bit on that last one, but you get the idea.