A lot depends on whether the course is used predominantly for matchplay or not. For instance, the 18th hole might be the most difficult hole for all classes of golfer, but nobody is going to give it Stroke Index 1, because few people will ever get to use that stroke. At Alwoodley the 365-yard par-4 12th is Stroke 2, but it is not a particularly difficult hole, and certainly not as difficult as any of those which follow it, which are rated 11, 9, 15, 4, 13, 7.
Because of our liking for matchplay, most British courses are given stroke indices with the odd strokes being taken on the front nine and even strokes on the back.
I took a browse through a few British score cards and, on the whole, most reserved Stroke 18 for their shortest par 3, others for a short par 4, while one or two allocated it to a short par 5. I didn't notice any on which Stroke 1 was a par 3, but I suppose there's one somewhere.