I agree that the right trailer is a matter of personal choice and that your needs are determined over time and and may also change with time. We have no dogs or children companions but will share our thoughts on our perfect TT. Keep in mind that we also started with a tent, pop up, hybrid, 25' no slide and now have our current model. As the OP stated, budget is obviously a consideration but there does seem to be some decent deals out there if you have the time to seek our what you want.
For the past 3 years we have loved our Outback 300RB. Why they discontinued this model is beyond me. My only thought is that at 34' long, perhaps most couples will opt for a 5th wheel. My wife talked me into it, I thought she was nuts until...
Length - 34 ' roughly. To date we have not had issues with many sites but keep in mind we do not camp in many state or national campgrounds in the US, yet... With the proper hitch and WD system, we have had 0 issues with towing. This size TT allowed for the following which are very important to us.
Bathroom - One of the largest we have seen. Enough said.
20' slide - I think that is what it measures. This is on one side only as we enjoy setting up our picnic table under the awning. Yeah we are spoiled inside but do prefer to eat and spend most of our time outside.
Bedroom - slide allows for a walk around bed which is critical for us.
Storage - too much, is that possible. Enough said
Outside kitchen - My favorite feature. 99% cooking and eating outside for us.
Use of truck - I typically bring my dirt bikes on the trips so using the back of the truck bed is essential. I am not sold on using a large part of a TT for storing toys.
For us, its important to be as comfortable in our TT as we are in our home. Some say that's not camping but for us, camping is seeing new places, spending time cooking and eating outside, having a fire and then a nice comfortable nights rest.
Best of luck with your search.
Oldcow
2013 Outback 300RB TT
2010 Tundra