We have a fairly wild yard that's hilly, inaccessible to a riding mower in some areas, partially wooded, etc. Overall, it's 6.5 acres with about ~3 acres being forest.
I have an 80s or 90s John Deere riding mower with a hydrostatic transmission. No idea what the deck size is, engine type / HP / etc., but it cuts very well.
To supplement that, we recently bought a 22" Craftsman self-propelled walk-behind mower with a Honda engine. It replaced our 3-4 year old 22" Craftsman self-propelled with a Briggs & Stratton engine and a busted gearbox. The new one is nice, but the older one did cut better (except you had to drag it backwards D
We also recently bought a 29cc 4-stroke Craftsman straight-shaft trimmer. It's decent, but tall, thick grass tends to get bound up just above the cutting head and needs to be cleaned regularly. :|
Finally, we have a DR Field & Brush trimmer, basically a weed whacker on wheels. It does a pretty good job at knocking down grass that's way overgrown (think two feet high) and very small undergrowth, but it tends to throw line regularly.
Overall, it works out pretty well. None of the pieces of equipment are perfect, but they all compliment each other pretty well.