I bought a 2.5 ton tandem trailer, and wanted to keep my 750 kg un braked single axle scrap trailer: My Volvo doesnt have a pickup bed to throw small stuff in, so when moving stuff just too big to fit in the trunk, i'd like to have a smaller trailer thats low and more narrow than the car, because it reduces fuel consumption because of weight and wind drag. However the small trailer (used as a mobile scrapbin the past few years) gets so bad that its time to leave it at the scrapyard the next time i haul scrap...
I cant have it all, so i'll stick with the tandem. I think the fuel saved from using the smaller trailer for light loads, cannot pay for refurbishment of this piece of junk to keep it on the road.
Dont know what you'll use it for, but it never hurts to buy a little more than you need, if its within the tow rating of your vehicle. In your case, you need the physical size anyways to put your stuff on it, so the weight and wind drag differences will be minimal. Go for the tandem !