I am currently on a contract with the walking floor moving rotting landfill waste from south London up to Manchester! It stinks, I get covered in crap, and I can’t get rid of the smell!!
The cleanest for me was containers full of dried fruit!
clean: trunking for a parcels firm
Dirtiest…my current job,hauling live chickens,you wouldnt belive how much crap a little bird can make,then times that by 6500 birds each load=loads of mess…and i get the pleasure of washing the whole wagon after every load 
Cleanest…Delivering bread,nice clean trailers and the load smells lovely 
cleanest. drive to Hemel Hemstead, undo doors on a box van, go to sleep, 3 hrs later close doors, drive to Athens via a ferry from Italy to Greece. Undo doors in Athens, go to sleep for 2hrs, close doors, back on ferry, drive to Prato Italy, undo doors, sleep/snooze for an afternoon while i get loaded, close doors, drive to Newcastle, undo doors, go to sleep for 3 hrs, close doors and go home.
Dirtiest. probably stripping dirty tilts out in the rain/snow.
Cleanest - working on the containers, cab was spotless all the time. 
Dirtiest - working on bulk tankers in and out of quaries, no matter how tight you had your windows closed always seemed to get dust and crap all over the cab. and your clothes were minging all the time. even with overalls on 
Cleanest; flicking four switches to lift the rollers to load / tip airfreight pallets
Dirtiest; Either tipping hanging meat at Smithfield. The fat and blood gets under your nails and the smell lingers for ages, or chaining down warrior APC’s to a low-loader in the rain. (mind you, got pretty black sometimes buggering about with a tilt)
cleanest probably the touring work i do
dirtiest would be hooklift containers on landfill sites. loved the job though
Cleanest hauling tarmac to main road resurfacing jobs.
Dirtiest hauling bulk slag from a steelworks on a tipper to a tractor and spreader 100 miles away.If you were overloaded at the Steelworks,you shovelled it off manually.No health & safety then.
cleanest job - Milk tankers ,secondary haulage between dairies ( loads of whole/skim/ buttermilk/ cream from dairy to dairy)
Dirtiest - 18 ton rigid delivering 50 kg bags of cattle feed to farms - but it kept you fit as a butchers dog.
Cleanest, my current job, I’ve had the same pair of gloves for 3yrs and they’re still like new, I hook up to a trailer, go down the road for 2 or 3 days open the doors once to tip and once more to load then 2 or 3 days back to the yard and drop it 
Dirtiest has to be when I was doing BSE offal and had to wash the trailer out after tipping it, sometimes you’d get a lung or some other piece of cow snot hanging over the brace bars in the body and you had to pull it down by hand, always made a bit of a splash when it landed 
Opening the back door could be tricky too, 200miles of running cross country in a 144 Scania with a log book, no limiter and me in full on Colin McRae mode used to stir up the load a bit, sometimes you’d get a face full of snot when you undid the twistlocks and broke the seal on the door, not the most pleasant experience 
cleanest job for me was when i was on fridge vans and the dirtiest was on low loaders
Dirtiest landfill work but good money. Cleanest general haulage with a curtainsider but that ain’t to clean
cleanest, driving a chocolate tanker, or possibly a covered car transporter.
dirtiest, running RVO from Robbie Dwyers to Grannox in Widnes
cleanest iv’e done is milk tanker trunking from devon to london,
the dirtiest is what i am on now, waste plaster board that we do from ridham docks to avonmouth the dust gets everywhere, even after a shower you still feel dirty after being back in the cab for 5 mins 
Cleanest down to Barcelona tip and load on same bay then back.
Dirtiest is a toss up between the walking floor I’m on now carting varying different kinds of crap or like wheel nut running in and out of granox at widnes - good times though 
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Simon.
Dirtiest: Sevalco in Avonmouth, loading tankers with carbon. You look dirty for weeks, you wouldn’t believe this stuff gets to.
cleanest was delivering parcels for UPS and the dirtiest , driving a sewage waste tanker, once, when i went to empty a toilet tank on a site i undone the clamps on the tank to enable me to then clamp the end of my hose onto it and it was so full that the pressure had built up and it erupted into the air and i couldnt get out of the way in time, it covered me from my chest right down my leg and it was only 10.00 am, i stunk all day even after trying to hose it off. disgusting. lol
Cleanest But seriously boring): Freezer work I do now and again at the moment. (In between live birds for a well known turkey breeder in Norfolk!)
Dirtiest: Bulk tyre black loading into flatbed trailer with tarps (curtains for you cushy types) on the inside of a set of 6’ gates out of Sydney and down to Melbourne. After loading I used to look like a coal miner… Not a good look when you need to drive 700 kms to Melbourne.
Cleanest: Night trunk driving for Parceline.
Dirtiest: Waste food skips for Sugarich. You’d be walking around in 2 inches of slop at the yard where you had to open the flaps to tip. At the collections, you usually had to shovel waste food into the new compactor when you did a change over. The stench was horrible but you did get used to it.
For some reason I actually used to enjoy the Sugarich job, maybe because there was no rushing about. I did it on agency so I think the longest I’d do was 3 or 4 weeks straight. In a strange kind of way it made a change to normal general work.
Containers ,clean-tilts grubby!