What is important to you? You only live once and if you spend most of that time being miserable what is the point of it. You have jet hours in a type that you can't get a better job on the same type, cant switch type as like you say type experience is required.
The way I see it is like this.
You have jet hours and are in a position to get some more if you stay put. Will more jet hours on a type you can't get off be useful. Probably not.
If you take the TP job I expect you will have a happier more structured life. You wont lose your jet hours but you will lose your currency on that type, which you can't get a job on anyway at a better company.
If you take the turboprop job I assume it is with an airline so you add airline ops to your CV.
If you take the turboprop I think your total time will increase much quicker.
When the industry picks up you still have your jet time, more total time and experience in an airline.
I don't think going from a jet to a turboprop is a backwards step. There are so many idiots in this industry that just have to get into a jet even if they are prepared to earn less than the person who cleans that jet. That is what is wrong with this industry, the
who spend £150,000 to get a job that pays £1500 a month, just so they can post a pic of themselves in an A320/737 on facebook to impress their mates. Pathetic.
Its about quality of life in the end, doing what you want to do with your family and friends, who cares what you fly you should be more focused on getting a better job that fits the lifestyle you want. If everyone who got into this industry did it for quality of life, things would be very very different and you would not have the kids working for peanuts or the turboprop captain wanting to get into a jet even if it means a paycut and reduction in quality of life.
Take the better job, that's my advice.