We have a RTT buyers guide with specs, pricing, sizes, fabrics etc going up tomorrow which should help you to decide, just check the front page in the morning.
I would say there are plenty of options, but you really need to consider your personal needs. Ex -
How often do you camp? If you're living out of a tent 150 days a year youll need better materials and components to stand up to the abuse. If its a weekend here and there some of the other cheap options might suffice.
What weather conditions do you camp in? - If you live in a desert where it is usually warm and sunny or you only camp in good weather water proofing, mold resistance, and breath ability might make less of a difference. Once again cheaper options may be okay. If you are camping in snow and rain you might want to consider things more closely
How many people do you want in the tent? - Most larger tents gain width, not length, so getting the biggest model might just add weight and make it harder to keep the tent warm with two people while not giving you much more head room.
You mentioned you are putting the tent on a trailer - if the trailer is the only mounting platform, there are more options than traditional roof tents - maybe you want a trailer tent from someone like kakadu.
Do you need to buy new? Used roof tents can be significantly cheaper and allow you to get a better quality product for a lower price.
There are plenty more factors to consider but these should get you started. What I will say is that MANY roof tents are made in the same Chinese factories and while their quality might be fine for the weekends here and there, they don't hold a candle to higher end tents. NOT ALL ROOF TENTS ARE THE SAME regardless of what people tell you. Spend a few night in an Eezi-Awn or a James Baroud then swap to a chinese no name and you will understand. Some of the chinese made tents are improving, using better fabrics and materials, but you need to research this.
The bottom line is that the right tent for me probably isn't the right tent for you. Like anything you consider buying, simply ask does it really fit YOUR needs? Don't listen to the BS that you need the best of the best for everything, sometimes a mid range and occasionally even a cheap option works just fine
