I have both a 25 gallon, tow behind sprayer with a 12 volt pump and a short boom that I use for herbicide and a 55 gallon single pole broadcast, PTO sprayer that I use for insecticide. For me it all depends on what your land is like. If it's relatively flat and smoothe, the tow behind works well but in the pasture, where it's much rougher, it tends to get beat up a bit. The 55 gallon PTO sprayer works anywhere although, with 450 pounds dangling off the back of my little tractor, it feels a little bit more "tippy" when I'm out in the pasture. Out in the pasture I prefer the 55 gallon sprayer because I dont have to waste time running back to the house to fill it up so often (basically, I guess I'm lazy). Around the house either one works well. I think the tow behind will cost more because of the trailer.
For herbicides I think I would prefer a tow behind because, with the boom and nozzles at a constant height, it's easier to get proper covereage. The PTO pump is more versatile because you can vary the pressure and coverage by adjusting the PTO rpm's. An electric, on demand pump works at a fixed pressure.
In the end it'll come down to personal preference, how you'll use it and cost. I know, I know, that's not much help, is it?