Pricing: There are no fees or commission on most markets (including stocks), but for crypto prediction markets Polymarket charges a small fee on takes (those that are not providing liquidity). So cheaper than dealing with a broker that is using a white lable.
Market Access: Loads of prediction markets on Polymarket with new ones being created daily based on political, sporting and financial events. If Polymarket does not display a market you want to trade you can request that they add it for you.
App & Platform: Very good for novice users, a simple interface and basic app make finding and predicting a market simple. There is API access for more experienced and professional traders.

Customer Service: Obviosuly no phone number to call if there are problems becuase this is 2026 and Polymarket is a massive fintech.
Research & Analysis: Brilliant, their Linkedin feed where they post interesting stats about probabilities is a great way to source ideas. Polymarket (by the very nature of their product) have some exceptions data points that they share with major news and research outlets for external analysis.