Rollups pack a bunch of transactions into one calldata that lands on L1, so you keep that rock‑solid security but get a huge speed boost—think of it as a supercharged highway that still uses the main road for safety. Sidechains spin off their own consensus, so they can be lightning‑fast but you’re trading that security for extra flexibility; it’s like a private track that might split the community. For most users the sweet spot is now rollups—mass TVL is growing fast—but sidechains still shine where custom logic or instant finality is king. Keep watching the TVL charts and the validator counts; that’s the best gauge of where the market’s leaning.