That's a great question. You could rephrase it, "What did/do you want in your second /next trailer."
My wife and I just became empty nesters. Our college girl might camp again with us, but not often. So our Scamp
16 is looking a little bigger than necessary. We might want to exchange that front bunk for a dinette, or a bathroom. And I'm still looking for a wider bed, where we don't have to sleep a'spoonin' all the time. So if we found a trailer with those features, I'd consider a trade.
Look at your own priorities. Do you need to park it in a small space, or fit a growing family inside? Would you rather have to cook outside. or have to pee outside? And always, how much weight
should you tow?