Fit and coverage come before waterproofing
A raincoat that fits poorly will make a rain-averse dog dislike walks even more, so start with fit rather than fabric. Look for a coat that covers the back and belly without restricting the shoulders or hips, with leg openings large enough that the dog can move freely at a normal gait. A hood is useful for dogs that hate rain hitting their head and ears, but only if it doesn't block peripheral vision or hearing, which can make an already nervous dog more anxious.
Waterproof vs water-resistant matters
"Water-resistant" fabric sheds light drizzle but soaks through in sustained rain, while genuinely waterproof fabric, usually a coated or laminated material with taped seams, keeps a dog dry through a real downpour. For a dog that already dislikes rain, staying properly dry matters more than it might for a dog that tolerates getting wet, since a cold, damp coat against the skin is its own source of discomfort on top of the noise and sensation the dog is already reacting to.
Practical features worth having
An underbelly strap or wrap-style closure keeps the coat from riding up or twisting during a walk, and a coat that's easy to get on and off quickly matters a lot for a dog that's impatient or anxious about the process itself. Reflective strips are a genuine safety benefit for dark, rainy walks. Avoid coats with loud fabric that crinkles noticeably with movement, for a sound-sensitive dog, the coat's own noise can add to the stress of the walk.
Introducing the coat calmly
For a dog that already dislikes rain, the coat itself can become a second thing to dread if it's only ever put on right before a stressful, wet walk. Practising putting the coat on indoors, in dry, calm conditions, with treats and a short positive session, helps separate "the coat" from "the unpleasant weather" in the dog's mind before you need it for a real walk.
When it's more than just dislike
Some dogs' reaction to rain is closer to fear or anxiety than simple preference, trembling, refusing to leave the porch, or trying to bolt back inside. A raincoat can make the walk more tolerable, but it won't resolve an underlying fear response on its own; if the reaction seems severe or is getting worse, it's worth discussing with your vet or a behaviourist alongside any gear changes.
Where possible, check a return policy or try a coat in-store before committing, since fit and noise tolerance vary so much between individual dogs that no single recommendation works for every dog. A coat that solves the rain problem but adds a new stressor of its own isn't really a solution, the right one should make the walk easier, not just drier.