free version
WP RocketWP Fastest CacheWP Super CacheW3TC
Database optimizationN #1 plugin for Database optimisation.premiumpremiumMM
Image compressionN 100% free, no limits*MRequires a separate pluginpremiumMM
Page cacheN At least as good as every other caching plugin - see benchmarking results premiumNNN
CSS and JS minificationNpremiumNMN
Mobile specific cacheNpremiumpremiumNN
GZIP compressionNpremiumNNN
Preload cacheNpremiumNNN
Simple setupNpremiumNMM

* most other image compression plugins have a monthly limit