Rubbra is an interesting composer. My own experience was that I found his symphonies quite plain when I first listened to them, but there was something about them that drew me back, and when I listened again more carefully I found a lot of depth. In that way he reminds me of Brahms, though on a more modest scale. His dense, polyphonic style is also quite Brahmsian.
Another thing that I find very attractive about his work is that it is influenced by Renaissance or Tudor music - someone described his symphonies as sounding like "vast orchestral motets" & I think that's about right.
I haven't heard all the symphonies, but of those I have I like nos. 4 & 7 the best. The 4th has a lot of that archaic quality in it, particularly in the 1st movement. The 7th is his most Brahmsian symphony, very stern with a passacaglia finale, a lot like Brahms' 4th.