I always say April is the best month for photographing warblers. When they first arrive on territory they show themselves more and there are less leaves on the trees to hide behind. This year the trees are very slow to green over, especially the oaks.
The easy two are Chiffchaff and Willow warbler, except the Willow warbler is getting harder to find as they become less common.
Blackcap and Garden warbler are more difficult as they do like the shade and dense vegetation and again the Garden warbler is getting scarce.
Wood warbler are on about the same level of difficulty as Chiffchaff, except there are only a few places you can go to find them. I did better with Wood warbler last year at the same place.
Here are this years April efforts.