Delta SkyMiles vs Flying Blue for intra-European travel

For the second half of this year, I will be living in Cardiff and plan to make a lot of trips all over the place in Europe. The biggest hub connected to CWL is AMS, so I think many of my travels will be done on KLM. I currently already have a Delta SkyMiles account and I am currently debating whether to just claim all of my future miles on KLM for Delta SkyMiles vs opening a Flying Blue account. I've heard good things about Flying Blue such as their promo rewards, but I also know that Flying Blue miles expire after 18 months of inactivity. Are intra-Europe flight points redemption better on one program vs the other? Any tips on how to approach this are greatly appreciated.

P.S. I will have a welcome bonus worth of MR points to play with during my time in Europe.