HC-110 was my only developer for a long while. I never was able to get it to work well with HP-5+ however. I like fine grain and lots of subtle gradation in the mid tones without blown highlights. I had completely given up on HP-5+ untill I got two rolls free with a packet of Ilford enlarging paper. Well, I processed those in D-23 and never looked back. This combo is so good I went out and bought fifty rolls of HP5+. There is no loss of speed. There is no loss of gradation. I get brilliant whites without blown highlights. Just wonderful (am I gushing?). I have a fresh bottle of HC-110. It only gets used with Tri-X and occasionally some FP4+ but, HP%+ always goes in the home brew D-23.
So, if you want big ugly grain, muddled tonality or blown highlights shoot HP5+ at less than box speed and dev in HC-110 (more dilution gives more grain). If you're looking for subtle, rich gradation and fine grain at full box speed go with D-23 (and don't over agitate).
There are millions of opinions here about what's good and what ain't. I have gotten some pretty good (in my deranged opinion) results with HP5+ and HC-110. I like to increase the dilution of the developers that I use in order to get longer developing times for my film. I also reduce the rate of agitation given in order to help avoid blown highlights. If you have access to a copy of "The Negative" by Ansel Adams, the revised edition that came out in the early 1980's, he details a way of using highly diluted HC-110 with reduced agitation that acts as a semi-compensating developer that retains good highlight detail.
If processed correctly, carefully and consistently, excellent results are possible with the HP5+ and HC-110 combination. It is my belief that reduced agitation also helps keep the grain from getting ugly.
I have used D-23 in the past, I feel that the grain is too mushy looking for my taste when used full strength. Again, this is a highly subjective area and you may not like what I like. I feel that there is too much sodium sulfite in undiluted D-23 to get what I consider acceptable sharpness, and I personally would use it diluted 1+2, testing it first on an unimportant roll or two to find the ideal film speed and developing time for my needs.
Just my 2 cents...
Mike Sullivan