The Manix is great. A bargain. It is big and beefy, but is still a great cutter, and a great *slicer*, which is something you can't say about many big, beefy knives. It is a great work knife if you want slicing ability in a beefy package.
I have handled a Lone Wolf Harsey Tactical Folder. Yes, the big one. It felt very stout. It is very large, making the Manix, Skirmish, and Rukus all feel small. Lockup was very good. But I have never used the knife. If you want a really big folder that isn't Cold Steel crap, it's one of the best choices, IMO.
I have a Skirmish, and it has tons of personality, but some minor faults. The lock is very stiff, and I have noticed this on all 4 Skirmishes I have handled. This can be a good thing, but it makes unlocking a chore. The titanium also shows dirt, ink, and scuffs very easily, making it not such a great dirty work knife. It is a strong, big, beefy folder that is also beautiful, but isn't as "all business" as the Manix. It isn't the most utilitarian knife you can buy, but it is very capable.
The Strider SNG and SMF are acclaimed... and sometimes called overrated. Never handled either, but I really want an SMF. In general they are considered tanks, but lack slicing ability. If you want something really tough and don't mind if you have to work a little harder to cut something (keeping in mind the wider edge is tougher), these might be for you. Especially the larger SMF. Expensive, though.
Handled a Rukus. Beefy and fairly classy. If you want easy opening and closing, this may be the one for you. It is much easier to open and close than any other knife I have mentioned.
Also look at the large Emersons.
Maybe the Benchmade 710 or 806 AFCK? They are great knives if they are big enough for you.
Depending on just how big your hands are, the Al Mar SERE 2000 and Spyderco Military might fit the bill as well.
Can't go wrong with any of these. I suggest you handle as many as possible to find what fits your hand. What is "really big" to you might just be a SERE 2000 to us. The smallish (in this company) Military might be big enough for you while something like the Lone Wolf Harsey is just rediculous big... bigger than you thought it would be.
One of my bosses at work once commented that my SERE 2000 was "a really, really huge knife". And he has bigger hands than me. When he asks for a really big knife, a SERE 2000 is what I would give him since he has never seen a Lone Wolf Harsey Tactical Folder.
p.s. I can flick a lockback closed much easier than a compression lock, and about equal to an Axis lock.