I personally think the 25' is an excellent size. But then, I have a '87 25' Sovereign
. We tow with a 1/2 ton Chevy pickup with the 6.5 diesel and 3.73 gearing. It is... adequate.
You will want to check the weight of your Thor against the 25' Safari and Classic to get an idea of how they will tow compared to your current trailer. I think the Classic is really nice, but I don't think I'd want to tow one without more truck and gearing. My '87 is more in line with the Safari on weight. Aside from weight, the Airstream will tow much, much easier at highway speeds than your white box. That stuff about aerodynamic shape is not just marketing. And the shape is not all - they are very clean aerodynamically underneath as well.
Overlander64 makes some really good points. And it does seem that 25' units are hard to find on the used market. Surely that will start to change with the success of the Safari.
Nothing as complex as a travel trailer is ever going to be problem free, but there is very little to choose from across the model years as reguards quality. In my opinion. Keeping in mind that there is zero chance of me buying a late model anytime soon. Different features, to be sure. Trade offs, to be sure, but in actual overall quality, it is hard to make the case that years XXXX to XXXX were somehow significantly better or worse.
To say that the vintage units were no better built is fight'n words in many quaters, and I don't want to fight. I also think it comes down to personal preferences. Yes, I'd like the thicker aluminum that will take a high polish, but then, I insist on a gray water tank and a rear bedroom. To aficianados, the 60s interiors are spare, and clean. To me they look like, well, lets just say I do not find it appealing and leave it at that. Yes, there have been some real mistakes made in recent years - the sagging headliners from the late 90s, eg, but what about the cracked interior endcaps for all of us 80s model owers? What about tail droop from the 70s? What about the polybutylene fiasco? Then there are 60s models with their $500 replacement door locks (although that is not really a quality problem).
It seems to me that you have to look at what issues are important to you, because you are the one that has to live with it. This forum is undoubtedly the best place to do that research.
In 2023, people will be on this forum, or one like it, discussing their 2003 Airstream. Few, if any, other makes will be able to say the same.
Waiting to stand corrected,