I like open trailers. I think they are the most productive since the equipment is already outside. Just grab the gas, trimmer or blower off the rack...no walking inside a trailer then back out. We mow 4 days per week, and leave the mowers on the trailer for 3 nights in between. They go in the garage the other 4 nights. And they go inside if it rains. The handhelds go inside every night. Open trailers are cheaper to buy, simple to maintain. I can dump materials on them, I can load pallets of stuff, or large b&b shrubs and trees on them with a forklift at the supplier. One of mine was even used as a parade float once.
Security is the biggest negative. Having those trimmers and blowers on display for thieves is not good.