TypeScript Alone: Uses tsc or esbuild for compilation. Slower but mature, supports all TS features. Best for small/medium projects or when simplicity is key.

TypeScript with SWC: Uses SWC for faster transpilation (10-20x faster than tsc). Less mature, may miss some TS features. Best for large projects needing speed, often paired with tsc --noEmit for type checking.

When to Use:

TypeScript Alone: Default for most Vite projects, especially if simple or using advanced TS features. SWC: Use for large projects with slow builds, but test compatibility and consider tsc for type safety.