Generally, the higher production volume, the more difficult it is to ensure consistent quality control.
I had a Keystone Vantage at one point, and it was a fairly decent trailer with few problems. But it cam out of a dedicated plant that only put out a few hundred units.
Jayco has a fairly good reputation, but all makers are putting out alot of trailers these days to meet the increased demand. So temper your expectations for perfection out of the gate. They all have warranties, and if you have a good dealer, he will take care of any problems promptly.
The advice I usually dole out is that it's more important to pick a good dealer above everything else - brand, layout, price, etc. It will make all the difference whether your purchase is a good experience or a nightmare.
To ensure you get a good one, be sure to do a thorough inspection and get all problems corrected before you take delivery. Once you are out the door, especially during the busy spring buying season, you will most likely have to stand in line to get any issues addressed. Search thru these forums and you will see what I'm saying.
Good luck!