Bitcoin is supposed to be trustless, but in fact you have to trust the miners, decreasingly so as they produce blocks; each subsequent miner who produces a block, confirms the work of the previous miner. So, at one confirmation you are trusting the miners 100%, at two its 50%, and so on.
In ripple (as I understand it), each ledger is final and cannot be re-orged, so you always have to trust the 'miners' 100%.
Bitshares has the same ever decreasing level of trust as bitcoin for block production, although I'm not entirely clear on whether the DEX means you need to place more trust in the delegates or not (I am ready to be corrected on this). My reasoning is this - since each block contains only transactions, there is no actual orderbook object with which to refer when matching orders, you can only build the OB up over time by processing transactions. This has the implication that, for any given market order in a block, each delegate would need to replay the entire blockchain in order to build the orderbook to process the order. This is impractical, so there must be some work around that delegates use in order to match orders and to confirm that the previous block contains valid matched orders.