Assuming you are in the UK.....
I can't speak for other instructors, but I used a CRP-1 for my PPL and a CRP-5 for my ATPL exams - the two are almost identical. I've seen E6Bs, but I've never actually used one. If a student comes to me with a question about a CRP-1 the chances are I'll know the answer. A question about an E6B, though, and it's unlikely I'll be able to help without reading the manual... and I may or may not have time to do that.
So my answer would be the CRP-5 if you have any thoughts of ever becoming a commercial pilot, or the CRP-1 otherwise. Stay away from the E6B - not because it's inferior (it may or may not be, I don't know) but because your instructor might not be as conversant with it if you have problems.
FFF
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