Depending on the type of 121 flying you have been doing be prepared for a culture shock. I was previously at a 121 ACMI operator so the changing schedules were not that much of a challenge for me.

It can be an adventure. There is good and bad. Probably the biggest change for you will be that you are going into smaller airports that do not have the infrastructure nor the operational standardization that you would be used to. With 135 you will not be sitting as brokers and the sales department are going to be constantly attempting to sell trips and keep the aircraft moving and generating income. There is a good chance with a 135 or 91K operator that you could be home based, so you will not have to relocate.

Corporate & 91 is a different thing and is usually thought of as being the "Unicorn Job", and pretty much what a lot of people aspire to. These jobs have their pluses and minuses as well, just as there is in every job. They are a lot more difficult to get and requires lots of politicking and networking. You may see advertisements for corporate jobs but what you have to understand is those jobs are mostly just listed as an HR requirement and they have already been filled internally or by people that have networked their way into the job. Corporate & 91 jobs usually require that you live in close proximity to where the aircraft is based.