George,
If you like the look of DDX, and you value a film speed increase (or at least no decrease), then you might look at Ilford Microphen. It is a phenidone-hydroquinone developer like DDX, and is said by some to give very similar results. There are a few here who really like it and can advise on speed, dev times, etc. for HP5. Personally I have not used it, but have been meaning to try it as a replenished developer for some time (just haven't gotten around to it as yet). There's a long thread here on Microphen with lots of good info if you're interested:
http://www.film-and-darkroom-user.or...ad.php?t=11350
But, as others have noted, if you ask a question about developer choice you will get a dozen different answers all based on the writer's personal preferences. Part of the fun of this hobby is to try different things, and film-developer combos are certainly fun to experiment with. I would say that changing the developer
can change the look of a film (just run one roll of HP5 in Rodinal and another in Perceptol and you will see what I mean). It's worth it to dig into this, decide what "look" you're after (amongst other variables - e.g. film speed, economy, etc.), and then zero in on a film-developer combo that will do the job.
Hope this helps...