Much prefer first half myself. On the Thames here from start of July to end of October there's almost always roach in all the roachy looking swims on most stretches with often dace, skimmers, perch, etc mixed in with all of them usually fairly obliging if the conditions are even half decent. Shoals of bream turn up in places and some stretches are crawling with pike. November onwards it's much more of a lottery with the fish getting super localised to patches of river with other bits seemingly devoid.