I'd second the recommendation of Sword and Spear Fantasy, based on the couple of times I've played it. Both games were good, and it's got a nicely "grounded" feel to it. By this, I mean that its roots as a historical game shine through - a good thing, in my opinion.
I have the Mayhem rules and have played them a couple of times. It's a very interesting game and offers a lot of flexibility to design your own units. The "danger vs default" system is unique, and the command system is innovative. I previously played it in 28mm, but will be playing it in 10mm once our forces are painted up.
One excellent option is Hordes of the Things. It's the massed-battle game I've played the most, and I can't recommend it highly enough. Games are quick and highly tactical, and the rules are pretty much watertight. If you like Dragon Rampant (which I do), HotT might appeal, as there's certainly some of its DNA in DR.
I can recall buying the HotT rules when they first came out, thinking it was an old game that I'd never heard of. We were playing Warhammer at the time and were fairly disenchanted with it (the ponderous turn system, the waiting for your go, the sheer time it took to set up armies, and the fact that games were almost never concluded in the available time ...). HotT was a revelation - we'd play several games in an afternoon, and the experience was far more tactical and challenging.
Which scale are you planning to use? HotT works really well in 28mm, because you need relatively few figures and only 3' square to play on. You can, of course, play much bigger battles with several players aside, or up the points from the standard 24AP to 36 or whatever. But it also works well in 15mm or 10mm. As you descend scales, it becomes less abstract in the way that troops are represented and more "massed".
The advantage of the more abstract approach (with, say, three 28mm figures representing one warband unit) is that you can get armies based and painted up very quickly. I'd imagine that most gamers have enough spare figures kicking around that they could put together a HotT army without much effort. And there's complete freedom to design your forces as you like. Here are
some of my chaos warriors, for example (classed as hordes in HotT), drawn from the dusty recesses of the lead and plastic pile.
Obviously, the qualities of all rulesets are subjective. But it's perhaps worth noting that - unlike many games - HotT has been going strong since its launch more than a quarter of a century ago and has only had
a single rule change in that time. That, along with its longstanding and enthusiastic player base, is a fairly strong indication that it works pretty well.
Edit: one other thing about HotT is that you can play a whole campaign in the time that you'd fit in a single game of many other rules. And figures based for HotT will largely be useable in S&SF, DR and Mayhem (doubling up elements) too.