The DA42 with Thielert engines was a delight to fly - smooth and simple to operate. The engine longevity seemed to be a problem. Ultimately their availability became a crisis.
The DA 42-360L was an improvement in many ways, engine history and reliability being chief among them. The compromise became economy, and a return to "old tech". The dependance upon 100LL another undesirable aspect. 180 HP a side sure makes for a great performer though! We did have one up to 19,200 feet during testing, but did not stay long enough to gather any cruise performance data.
I have great hopes for the success of the new diesel engines, but know nothing about them. Like any new powerplant, there comes the inevitable question as to how long you should wait/how many in service, before you buy in. It's a personal decision...
I also have great hopes for the SMA diesel, as we have an order in for one. Things are delayed, but my hope remains. Though I believe that Continental will market a good diesel engine too, I believe that SMA will remain well ahead of Continental for some time to come.
The future is diesel though....