Great that you mention it. I think the Fifth isn't reffered to that often among the Arnold fans here. But as it happened to be the first one I heard, somewhere around 1979 and in the EMI recording with Sir Malcolm himself conducting, I've always had a week spot for it. I vividly recall the thrill of it, especially when I discovered that I coulf find e.g. the final movement's theme "trivial", even utterly banal, and yet great at the same moment.
Arnold's been one of my elementary lessons in music, later learned from Shosta and Mahler and RVW 9 as well: how `banality' may be used to great symphonic effects. I love all Arnold's symphonies, the Ninth no less than the others. But the Fifth remains a first love.
I like the use of the word 'lesson' there, as I certainly agree Arnold takes some degree of personal study to really appreciate. Of course I don't mean
formal study, but rather patience and an open, enquiring mind. Taken at face value, the 'pop' tunes in his music can easily be taken as banal, but as you imply it is just a natural extension of what Mahler did in incorporating the 'pop' music of his time. Perhaps just because Arnold's tunes seem more contemporary we are more accutely aware of their contrast with the surrounding music, and to some ears that might grate. Certainly it took some years for me to come around to the 4th and 6th, which are almost schizophrenic the contrast being so severe. But now I love them as much as the 5th.
The 3rd was my introduction to Arnold and I still think very highly of it. I discovered it at a time when I was exploring golden age film music, and I thought Arnold's 3rd quite Herrmann-esque. Of course, I later to came to realise it was actually Bernard Herrmann who was an anglophile, and who was friendly with Sir Malcolm. So perhaps we might say Herrmann's music was Arnold-esque?

Yes, that's a disc I would recommend without reservation. A desert island disc for me maybe. The 5th is painfully touching under the direction of its composer, and Groves, as he did with so much music, injects an awesome intensity to the 2nd.