There really is no 'best' developer for theser films, or any other. I've found the differences between popular general purpose developers to be very subtle, at least for 'normal' photography, not pushing to higher film speed.(posted 9608 days ago)FWIW, Ilford has a table in their film data sheets that recomends a developers based on if you're trying to get best overall quality, finest grain, sharpest image, maximum film speed, cheapest developing, and so on. It's too much to type in here, but start at www.ilford.com and search on down for film product information, and you'll find a PDF file of film data which contains this table.
Also FWIW, I use Xtol 1:3 to develop HP5+ in 35mm, 120, and 4x5 formats. It works well for me esposing at ei 200. 18 minutes in small tanks, 12.25 minutes for 4x5 sheets in spinning tubes. The smallest quantity of solution I ever use is 450ml at working strength.