Welcome to the forum.
You might choose any of those. Petrol engines tend to be a little 'tired' after 200,000km although my Commodore (which I did look after very well) was still strong when I traded it on my (new) D40 diesel auto in 2009.
I am very happy with my choice. I bought mine because I wanted something to haul a fifth wheeler on the highway with an occasional sojourn into the forest which made having a 4WD beneficial as I had been stuck on the grass in the rain - the ground was ALMOST level but soggy and the Commodore had zero traction.
Of course once we bought the Navara we tried being a tiny bit adventurous and thoroughly enjoyed the additional freedom. We discarded the idea of the fifth wheeler because of articulation issues with our new-found adventuring - something in us that we had never discovered and as we approach our retirement it's something we were quite surprised to find, but having found it we're enjoying every minute, every waterfall, every stunning valley view, every quiet moment in a peaceful forest.
Ours is a diesel. It has the scary $4,000 fuel pump but 113,000km and it's not given us a moment's issue. I am a reasonably gentle driver, but that won't make a difference when crap gets in the fuel which is where more trouble starts. Add injectors + fuel rail and the price tag for JUST those components has been stated as somewhere around the $8K-$9K mark.
The diesel engines have also had scares with the timing chains. They aren't as strong as they ought to be, yd25.com.au sells a much-improved replacement item but fitting is a little time consuming - having a auto-handy family member saves there.
Petrol runs a cheap pump, can tolerate a little muck/water in the fuel, but you can't submerge the vehicle. Fuel usage is greater - up to 50% more. We've got guys in the forum with diesels of that vintage getting 10-11LPHK on a highway, and the petrols doing 15-16LPHK.
From a running-cost viewpoint doing a bit of highway travelling, 1,000km in the diesel will cost you ($1.50*10*1000/100) = $150. The petrol will cost $1.40*15*1000/100 = $210.
Putting that in perspective: driving from Sydney to Perth and back (8,000km) costs $1,680 in petrol or $1,200 in the diesel. An "average" yearly driving of 20,000km costs $4,200 in petrol or $3,000 in diesel. Over the life of my vehicle that's a difference of $23,730 in petrol or $16,950 in diesel. I've saved around $6,000 by buying a diesel.
It will take time to recover the cost of the pump/rail/injectors so if you look at the fuel pump/rail/injector issue and decide the risk isn't worth it, grab the petrol. Personally I'm not that concerned by it, if I was really bothered I'd fit a water trap and a second filter.
As for brands - ANY common rail diesel is like that, from any manufacturer. It's simply expensive technology. Navaras from that era stand out from the competitors in power and cabin appointments.
Suspension in both is an issue, so if that's been upgraded from stock it's one less thing to worry about.
The one other difference is noise. The petrol is quiet at cruise but you'll always know the diesel is running. On the highway the diesel is not bad, but there have been occasions when we've been desperate enough to try McDonalds and I've had to shut down the engine so I can hear the kids voice from the shitty little speakers.
The big question - which one would I choose if I could do it all again? Diesel. Every time.
