The represents a unique intersection of nostalgia and utility. It is a relic from an era when PC gaming was simpler—when you could download a 500kb file from a Geocities page and suddenly become invincible.
The "best" trainer depends on your needs. LIRW's +23 Trainer offers the most features, while DFSoeten's Trainer provides a simple interface for resource editing.
Using a trainer does not mean you have to strip the fun out of the game. You can use it dynamically to create unique sandbox experiences: