If you're a swap user: in most cases you don't need to pick a pool type manually. Omniston routing automatically chooses the most efficient path through the available pools for your swap, so the right pool gets used under the hood.
If you're providing liquidity: Stableswap or WStableswap are the natural choice for assets that move at similar prices (like stablecoin pairs) — you'll get minimal slippage even on larger swaps. WCPI is useful when you're combining very different tokens and want custom ratio control.
If you're a token creator: the pool type at creation is set up via the STON.fi team, not through the user interface — see How do I decide between regular, WCPI, or stable pools?