A personal thought.
For me, il2 is still number one. So far.. There is still a lot to explore. Unfortunately, graphics and technology are outdated, which means we may look after a replacement sooner or later, me think. I have wondered if BOS is a worthy follower. Have not tried it yet but as far I have seen, and heard, it looks good.
Personally, I like CLOD a lot but it's starting to be a bit boring to fly the same map and mission every time. Hoping for updates in a close future. If that happen, I will stick to Clod for a bit longer.
As for DCS, I'm not interested, yet, as it seems more like a flight simulator than a game like IL2. Or BOS. It's no as important for me to press the correct buttons, flip the right switches and be totally devoted to the realistics, like in DCS. I want varied missions, co-ops and maps. I'm for a continuation of IL2. It seems that it may be relevant to look closer a replacement for IL2 in the foreseeable future, though.