The wire has enough flex to eliminate and concern with connection due to vibration vibration.
Interestingly, there are actually MIL STD specs on wiring in high vibration environments that forbid the use of solder especially with stranded wire. In the experimental aviation community this is one of the first things taught for wiring a self-built aircraft. The solder can wick along the wires and extend the stress point out along the wire to a point where it's unsupported. That spot where it goes from rigid to flexible can stress-crack over time and lead to failures. It doesn't even have to be a total break. Just breaking a strand or two can reduce the overall ampacity of the wire and potentially even cause a fire due to local heating.
Solder is a rigid connection best used in rigid environments, like on circuit boards. I am personally a fan of those solder crimps as well and regularly use them in places where I shouldn't because let's face it, I'm going to tug the heck out of my trailer wires all the time, and if they last 3-5 years I'm way ahead of my average. But OP was asking for the best recommendations so from that perspective I guess a decent list would possibly be something like:
Wago - for Romex connections in a junction box in a light fixture or house. Electricians are having religious wars over these, especially since Leviton and others introduced this style directly in their outlets (and electricians were already having a war over "stab" connections so this was just more fun around the campfire)
Sealed crimp pin connectors - for automotive and trailer where you need a disconnect. Molex Mate-n-Lock, TE, Deutsch, these run hundreds of $ but you can find generics on Amazon almost as good. I love these and redid my truck with them recently but they're pretty overkill for something like a trailer.
Solder - Anywhere a wire connects to a board and will have vibration support PAST where the solder can wick, usually at least a half inch away. Simple, fast, cheap, and less prone to corrosion than other options.
Solder Sleeve - If you just need it to work fast, and you're tired of electrical tape. I do all my trailer harnesses with these even though you're not supposed to use them there. Get the adhesive-sealant kind. That adds vibration support and makes them waterproof. Worth the extra dollar or two per kit. These are PERFECT for emergency repairs because they're fast and melt at a low temp so even a lighter is usually enough to melt them. I keep a small baggie in every one of my vehicle gloveboxes/toolkits.
Crimp sleeve - oldies but goodies, they work fine and there's nothing wrong with them. The biggest mistake most folks make is trying to crimp them with pliers. Get the tool, it's worth it. To make a gas-tight seal you need to deform not just the sleeve itself but also the strands of copper getting crimped. It's really hard to do this properly with pliers because you need a sort of rounded surface pressing on the connector to do it right, it's not just about strength. Even a cheap harbor freight crimper is better than pliers.
Twist and electrical tape - hey, it's not "wrong", it's just "ghetto." It does work in a pinch...
I personally wouldn't use dielectric grease on a connection like this. It's meant to protect pins in terminals, not wire connections themselves. I'd rather use an adhesive solder sleeve even if it was "wrong" on paper.
