On Bitshares DX you are only trading and IOU representing an asset. There are some liquidity issues (bitBTC trade volume is not that much. Not completely trustless as you have to trust whoever holds those assets don't default.

On Blocknet DX you trade the actual asset. This has higher technical requirements (you currently need to be running full nodes to trade. But it should be much better once we can use SPV wallets (lite wallets)). You are in complete control of your coins; it is fully trustless.

For me Blocknet is definitely better tech from the decentralization standpoint (kinda a core tenet of cryptocurrencies in my opinion), but could be less user friendly for now. I believe Blocknet is still highly undervalued.