Decentralised: - cant handle high load, low liquidity, risk of poor implemented systems locking or losing tokens with no one taking responsibility. No fiat gateway likely. Bypass KYC/AML so regulators may see as threat. + bypass KYC, no limits on withdraw amounts, lower risk of direct hack
Centralised: - higher risk of hack, also can have low liquidity and struggle with load, rubbish support not taking responsibility. + can support high load and liquidity, regulatory compliance offers mainstream adoption. offer some support.
Really it doesnt matter the model used, unless they are well designed amd implemented in terms of code, infrastructure and support, they will be poor. centralised exchanges have the opportunity to be better as there is more interest (profit) in producing a stable, quality platform. decentralised is nice for the purists and potential to be better *if* someone puts in the effort without reward to build it properly.