We own a 2015 Thor Siesta Sprinter 24ST Model.We love our rig, have had very few issues, none after purchase requiring Thor warranty work. We have had a very good experience.
With that said:
We took time going over our rig after we decided it was the one for us. Created a list of items to be completed by the dealer BEFORE we took delivery. We took photo's and videotaped as needed. All of the items were minor fit and finish (except for a small exterior paint chip) and addressed. We took 2 extended pre-purchase rides.
I have heard both good and horror stories about Thor products. After reading as much information as I could get my hands on for the first 2 years, I believe all brands have quality control and finish issues. A few higher $ end companies have few issues. Most of the mass producers have issues,some more than others.
DH & I attended many RV shows from 2011-2014. At most shows, I was suprised to see poor quality in better known brands.
Good luck with whatever you choose. Use the knowledge you've earned from your current rig, it should serve you well.