I'm a lot more concerned about your application than I am about wafer or lug connection. To paraphrase what was stated earlier: Lugged valves are for the guys who work with them, wafer valves are for purchasing clerks.
Butterfly valves in abrasive slurries can be great or they can be a disaster. The original rubber-lined butterfly valves were developed for cement dust. A cast-iron vane and a rubber liner lasts pretty well in that application. There are also rubber-encapsulated vanes to protect against abrasion. They make tires out of rubber...abrasion resistance is one of the primary reasons. Automotive brakes are made of cast iron for the same reason. The best trick for ruber-lined valve in abrasives is to undercut the vane: i.e. to reduce slightly the diameter of the vane, so that the vane does not grind grit against the seat with ans much force as a standard-fit valve would.
What is the temperature of your application?
What is the flowrate in your application/line-size/velocity?
High-performance (double-offset) valves are not as successful in abrasive services as symmetrical butterflies. The seating surface on an HP valve is narrow and must be polished. Turning the vane with the finely-polished edge facing directly into the abrasive flow results in the finely-polished surface not being there for you when you need the valve to shut off. The seats are usually convoluted to be process-energized. Packing the convolutions with abrasive fines does not contribute to their successful functioning.
Triple-offset valves seat without wiping action, so they tend to trap chunks between teh vane and seating surface. There is an active sealing member in most TO valves (One MFR calls it a lamellar ring) , and the crevice between the active sealing member and its holder can pack with fines. Again, if this gets chewed up in the open position, the valve will leak when you try to close it.
If your slurry temperature is compatible with elastomers, use a rubber-lined valve.
Try to keep the velocity between the values where the particles drop out, and an upper limit of around 12 FPS.
Earlier advice about having the stem horizontal is valid. ALSO put the actuator on the left side (looking downstream). Actuators customarily open CCW, so this installation will push back/dislodge/flush the settled layer of sludge at the bottom of the line as the valve opens.
One other trick is to put a 1" thick steel plate in the pipe upstream of the valve, in the same plane as the open vane. This will work like an inertial cleaner, deflecting the larger chunks and allowing the open vane to stay in its protective "wake". This will protect the LE of the vane and help extend the life of the valve. It needs to be as close as possible to the valve, but make sure you can get the vane completely open.
If the service is too hot for elastomers, think about a ceramic ball valve instead.