TL;DR included at the end.
For context, I'm posting this as a Lv54 player (all skills unlocked, and payout increases per level due to proficiency bonus),with all cities discovered (all DLC's except for Road to the Black Sea). The best freight market jobs (any trailer type) I can typically get are above 55 €/km, reaching up to 75 €/km if I get really lucky.
There are 5 trailer classes: FLB, CNT, STD, LOG, and FDT.
I just want to make more money! What should I get?
STD (curtainsiders, dry vans, insulated, and refrigerated/reefers) is without a shadow of a doubt the best class for making money.
Curtainsiders are a fantastic starting point for lower level players, with many cargo types that allow me to earn between 65 and 85 €/km. These were (highest paying options bolded):
Boric acid and performance forks - no skills required
Electronics, transmissions, diesel generators - high value cargo Lv1 required
Motorcycles , scooters , medical equipment , computer processors - high value and fragile cargo Lv1 required
Dynamite, ammunition, explosives, fireworks - fragile cargo Lv1 and ADR class 1 required
Upgrading to dry van is (probably unexpectedly) NOT recommended. The upgrade does not increase payout for any of these cargo types, and dry vans cannot ship the ADR class 1 materials.
Insulated trailers have a largely different set of cargo types; the only thing it can carry that was listed earlier is medical equipment, which still has the same payout with this trailer type. What gives insulated trailers a huge advantage over curtainsiders is medical vaccine cargo , which requires fragile cargo Lv1 and ADR class 6. Now this is where the money is; I'm able to earn between 75 and 95 €/km transporting vaccines (usually somewhere in the mid to upper 80s),and it's a very common cargo type too.
Upgrading to refrigerated is not necessary. Again, it does not increase job payout, doesn't introduce any new high paying cargo types, and is much more expensive.
But standard is too standard! Is anything else any good?
Well, if you really have to be different, a 3 axle FDT (food tank) can pay pretty well. Its only good cargo is milk ; which is the second highest paying cargo in the game...
...assuming you're in a country that will let you move 30t of it. Some countries have a 26t weight limit for these trailers. The countries a 30t limit are Luxembourg, Belgium, the Netherlands, Austria, the Czech Republic, France, Italy, Finland, Sweden, and Norway. Sweden also seems to have a higher 32t limit available for jobs that stay within the country, but I've only seen this available for juice concentrate, and am not sure if this applies to milk as well. Luckily, when you take one of these 30t jobs, the country you will finish in will always have the same limit.
[If anyone with the Road to the Black Sea DLC can check Romania, Bulgaria, and Turkey, please let me know if those countries have the higher weight limit as well.]
So just boxes and... milk? Isn't there anything a bit more interesting?
Okay, flatbeds aren't too bad for making money. They probably still average out a bit above freight cargo jobs, at least. And yeah, they definitely get a bit more interesting than boxes and milk.
There are 5 flatbed variants: wooden floor, steel floor, drop side, floor with container pins, and drop side with crane.
Wooden floor and steel floor are only different in name and looks; they carry the exact same weight. The issue with these is that they only have three high value cargo types: pressure tanks, train axles, and train undercarriages . I get paid anywhere between 53 and 70 €/km for these, usually in the mid 60s. Luckily these are incredibly common all across the map. All other compatible cargo types pay considerably lower.
Flatbeds with container pins are the best option in this group. Not only can it ship the 3 high value cargo types that wooden/steel floor trailers can; it also has access to many ADR class 2, 4, and 6 materials, many of which also require fragile cargo Lv1. A lot of these pay on par with the high value cargo, maybe even a tiny bit more. ADR class 1 also allows you to play makeshift fuel tanker for half-decent pay, if so tickles your fancy.
The two drop side variants are incredibly limited. They have very few cargo types, and rarely pay any more than 50 €/km. The crane variant actually pays less , due to it being able to carry less cargo. Pretty ridiculous given its price.
What about the other two trailer types?
LOG - Don't bother. Has 5 cargo types, 4 of which are shared with wooden/steel floor flatbeds. Only unique one is, unsurprisingly, logs. Doesn't pay jack diddly compared to any other trailer type.
CNT - Again, don't bother. Flatbeds with container pins can do all the same cargo types for higher payout.
And the other upgrades?
Articulated trailers (Double, B Double) - You can only get jobs for these in Germany, Netherlands, and the Scandinavian countries. A bigger issue with these is that they don't guarantee larger shipments, and for some cargo types even result in smaller shipments. If you're fine with this and just want a challenge, then go for it.
HCT trailers - Jobs are completely limited to within Finland. They can carry more cargo than Double and B Double, so the €/km is definitely higher, but I imagine being limited to one country will get old pretty quickly.
More axles - Increased axles only increases job payout for a few cargo types that are low-paying to begin with. If you want steering axles on your trailer, then go for it.
Tires - Better tires don't affect what jobs you can take, but of course, it doesn't hurt to have them.
TL;DR
BEST TRAILERS
For newbies - Basic single curtainsider
If you wanna make hella money moving vaccines all day every day - Basic single insulated
If you're a milk chugging freak - 3-axle food tank
If you're not boring - Single flatbed with container pins
Hopefully some people can find this information useful.
that said, I was expecting the ability to have more .... exotic cargo for those. It's just same old forklifts, boats and a few loaders/backhoes/excavators. I think I'll need to fetch the Heavy and Special cargo DLCs...