The Xantia probably has the best of the hydraulic suspension systems that were ever on the market (including MB, which is a ridiculously fragile system). The XM is more comfy but the Xantia is far more reliable mostly because it is a somewhat simpler system (cheaper car, so less complexity = more profit but incidentally also more reliability).

The very worst was the SM, which overcomplicated just about everything. If you open the hood on one you'll have at least six "WHY?"'s going through your head at once, the kicker being the rotating shaft over the top of the engine to drive a pump on the other side of the block.