You carry a topper with you all of the time, and it limits what you can do with your pickup. The trailer makes it easier to haul dogs, and doesn't get carried with you to work or wherever you take your truck.
If you need to use an ATV, either get ramps for your truck or set up your trailer to accept your ATV. My preference is to put the ATV on the trailer just to keep the bed of the truck open.
i have a topper. i like it because i take my dogs with me everywhere, every day and don't need to "hook up" to go. i am a general contractor and visit several jobs daily and the dogs are always there. i have incredible dry storage in my topper so i can carry work tools as well as training gear. i added verticle bars to the topper's rack and it handles wingers, ladders, canoe, rebar....whatever. it is like having a panel truck with ladder rack and dog transport. i don't find it limiting, i find it liberating! if i need atv i have a 6 x 10 utility for that.
if i used a trailer i would probably not take the time to hook up 50% of the time. i never get stuck on a muddy jobsite pulling a trailer and i have never jack knifed my topper into the side of my truck! lol
it's all a compromise, every person has different and multiple reasons for owning a truck. pick what's best for you!
I would be worried about the dogs in a trailer. It would have to be pretty big so that it wasn't bouncing around going down the road. I would miss having the bed of my truck but I think it would be safer to have a topper. JMO
my brother had a trailer for about a year...couldnt get rid of it fast enough, horrible ride, plus he soon figured out that he couldn't leave it just anywhere, the only time it came in handy was during a SoDak pheasant hunt where we had more dogs and hunters/gear to invade a small town...
for toppers its hard to beat Ainley,or Deerskin...sure there are others but am not familiar with them...
well here is what I have in the works. An 8 hole topper that breaks down in 2 pieces. a 6 hole and a 2 hole. I am also going to custom build a trailer to assemble the topper to with a spot for the 4 wheeler. so I have the option of using either one.
As well as the concerns and comments noted above, I have been into some test sites where pulling a trailer in and being able to turn around would have been impossible. That means parking at a distance and having a loooooong walk in .... not too bad if you are only running one dog, but if running multiple dogs would make for a very long day!
Topper. Better ride for the dogs, and its safer. They are up higher in case of collision and far less at risk in wind, on ice, or with hitch issues. I have a temperature monitor, too, that would be hard to wire in a trailer.
I have a smaller Toyota for work when the dogs stay home, but even without that, I drive the diesel with the dog box to work, shopping, etc at times just to keep the batteries charged and the engine working. The only problem that presents is that of any large pickup - its hard to park in small slots in a parking lot. If you're like me and bring at least one dog everywhere, having the dog box with you is safer for high temperatures if you want to leave the dog in the vehicle - can't leave one in the cab of a pickup in warm weather but with a well-ventilated box you can (I have fans, too).