Fred,
It depends on the type of fly I'm tying.
I use AJ standard irons in #1.5-7 with the #1.5's and #3's for spey flies with the #1.5 exclusively for winter fishing. I use the #5's and 7's for Irish Shrimp style flies.
I use the AJ Heavy wire in #3 for General Practitioners.
I use the AJ blind-eye #1.5 for dee flies.
I use Daiichi 2441, standard salmon iron, in #2/0 to #2 for marabou spiders, Ally's Shrimps (and Cascades), and large hairwing wets if someone wants me to tie them. I use this hook in #4-#8 for a heavier summer/fall Ally's Shrimp (or Cascade), strip-wing featherwings like the BLUE CHARM, etc., and hairwing wets.
I use Daiichi 2421 in #6-10 for Ally's Shrimp in low-water, Lemire's Grease Liner (usually I only use #6's for this fly), classic strip-wing featherwings in "normal" summer flows, and the smaller #8's and 10's for flies like the classic SUN FLIES and PIRATE or BLUE BOYNE series. I also use this hook to tie flies like Wulff's for steelhead, COMETS, and Wagner's LANTERNS and SUNDOWNER series.
I use the Daiichi 2131 (also known as the Bob Veverka Classic Salmon Hook and the Alec Jackson River Dee Low-water Hook) in all sizes for true low-water flies, and in #6 and 8 for a lighter dress dry fly.
I use the Daiichi 2161 (also known and the Alec Jackson Steelhead Iron) in #6 (Alec calls it a #9) the smallest size, for SPADE, original and variations such as Alec's GUINEA SPADE, etc.
I use Dave McNeese's Blue Heron hook in #3 for spey flies and a few classic salmon flies like the SILVER SPECTRE and other herl winged flies. I use this hook in #2 if I want a very large spey fly and in # 1 for dee flies. It is a lovely hook and I've told Dave I'd like to see it in a #4 as well for Irish Shrimp flies for summer.
I use Daiichi #2220 for WOOLLEY BUGGERS and its ilk and in #6 for BOMBERS. Although I will likely start tying BOMBERS on the Daiichi #2117 (black), or #2110 (bronze) Van Klinken Bomber Hook this summer for them because it has a wider gap and the shank length if virtually identical to the #2220.
The Daiichi #2371 (the Dick Talleur Classic Salmon Hook) makes for a lovely dee hook in #'s 2&4 and a lovely, straight shank spey hook in #/s 6 & 8.