It’s hard to say which are the best models of evaporative coolers. There are some customer reviews in Amazon or Home Depot, but they are only in the dozens, and involve mainly the more inexpensive models (portable evaporative coolers). They aren't of great help, except for some portable models.
Overall, these online reviews are rather mixed, with detractors and defenders. Even the best rated models have a significant number of unsatisfied buyers, with complaints about their low performance and, in more rare cases, failures…
Evaporative cooler brands and manufacturers
The existing reviews cover some top manufacturers and brands: Dayton, Essicker (brands: Champion, Mastercool, Essickair, Speckair), Kuulair, SPT (Sunpentown), Newair, Luma, Aerocool, Bonaire (Australia), Port-A-Cool…
Essicker produces a wide range of products and models, but others are largely specialized in portables (Kuulair, Sunpentown, Newair, Luma), central ducted models (Aerocool, Bonaire) or large mobile models for outdoor and open-space uses (Port-a-Cool)… These brands are mainly sold through local dealers, but also online and through big retail stores (Amazon, Home Depot…).
Portable evaporative coolers
Kuulair, Sunpentown, Newair and Luma are selling inexpensive portable coolers ($100-$150, online) with very mixed reviews. You can take a look at these coolers and to customer reviews and ratings at Amazon.com, here: Portable Evaporative Coolers.
Note: these coolers are mainly aimed to cool small rooms in moderate-hot dry climates. Many of them have a very low capacity, typically below 700 or 800 CFM (too low, for average needs in hot climates).
Window evaporative coolers
Champion/Essicker and Dayton are top manufacturers of window evaporative coolers. The best and most powerful of these models are able to cool small homes and large open spaces.
They are priced around $500-$600 in Home Depot and Amazon. Ratings at Home Depot are very mixed but overall favorable. There aren't reviews (or a significant number of reviews) at Amazon: Amazon Window Evaporative Coolers.
Mobile Evaporative coolers
The so called mobile coolers are mainly aimed for large open spaces like garages and warehouses. Port-a-cool – the bigger manufacturer on this category – is selling them through Home Depot and Amazon: Port-a-Cool, Amazon. There are few customer reviews on these expensive coolers.
Central Evaporative Coolers
Central evaporative coolers (either ducted or non-ducted) are mostly sold in local retail stores and dealers. But Home Depot is also selling the Champion brand, while Amazon is selling Champion/Essicker and Dayton models (see: Central Evaporative Coolers, Amazon). These models have few customer reviews, and their prices and capacity are mostly in the range $500-$800 and 4.000-6.000 CPU (1.000-1.250 sq feet homes).