Firstly, the primary weapon, Autocannon or Twin Lascannons; I think it would very much depend on what you want to do with the tank. Lascannon being the premier anti vehicle weapon of choice whereas autocannon is more anti heavy infantry and light vehicles. The choice of main weapon seems to determine the rest of the predator loadout.
Honestly both have their trade offs. The lascannon, as you point out, is better suited for anti armour given its higher AP however its rate of damage can be minimal at times. Conversely, the predator autocannon has a more consistent damage output, at the cost of shots fired per turn and a lower AP.
The two main kinds seem to be the annhilator or destructor loadout - 4 lascannons or autocannon + heavy bolter sponsors.
This was more the case in earlier editions, and though the triple las and auto/heavy bolter loadouts still retain their pattern titles they are interchangeable as predators.
From fourth edition onward, the auto-las predator was noted as being great for its versatility. It traded a lascannon shot in order to make the predator a bit more useful against certain elite troops or lighter monsters. Eighth edition, with the ability for a squad or vehicle to split fire its weapons across multiple targets, does indeed strengthen this versatility.
as autocannons are probably on the whole better than heavy bolters for a variety of roles.
This largely depends on what your shooting at. Overall though the two are fairly even, with the heavy bolter sacrificing some strength and damage output for a more consistent rate of fire. But if you are going to be putting any lascannons on your predator, then I would say your best off with las sponsons and the autocannon turret.
As chaos, I'm inclined to add the havoc launchers and a combi weapon of some sort. I am inclined towards a combi-plasma for anti-heavy infantry options. What do the other options offer?
Havoc launcher gives you the chance for a nice bump in extra shots, as for combi bolter I'd just say stick with the standard one. An auto-las pred is already running you 180 points, a combi plasma and havoc launcher pushes you above 200 (just taking the havoc launcher puts you at over 190 and the normal combi bolter is dirt cheap.)
Would love peoples thoughts on this. Also, given that a landraider is almost twice as expensive as a laspredator or a fully decked out auto-predator, which is better. 1 landraider or two predators?
While its true that land raiders are considerably more expensive than predators, you have to keep in mind what you get for that cost. In addition to more wounds, a land raiders toughness is higher, it has better armour, and can move and shoot its heavy weapons without penalty; plus it can also transport models.
A pair of predators would, mostly, come out to about the same as the single land raider, and the pair would have six more wounds and be able to pump out up to twice as many non lascannon shots. But when those predators take damage from the lascannons, their save is all but completely stripped. The land raiders armour would take a heavy hit as well, but a +5 is still a lot better than a +6.
Going by averages and statistics, the pair of predators should be able to remove 6-7 wounds from the land raider if they do not move (dropping to 4-5 if they both move.) The land raider, on the other hand, deals an average of 6-7 wounds between its weapons regardless of whether or not it moves. This means that between the two, the land raider would still be in its first profile bracket while one or both predators might drop to their second brackets.
For the cost and ability, Im a proponent of auto-las predators. But when it comes to land raiders, they are quite strong despite their cost. I've seen games where an entire army lays all of their guns into a single one to take it down, essentially leaving some 75% of your army untouched in the shooting phase.