I've always bought Practical Photography. There seems to be lots more in it every month, and it's more varied imho.
Though they both have Photoshop guides, the Digital Photo guides always seemed to be gimmicky type things, and the Practical Photography topics were generally more useful. Recently, either because they feel they have covered the basics of Photoshop or the thing that people want the gimmicks. they are drifting more towards the Digital Photo mag guides. :bonk:
Best way to decide is to go into a shop and see which you prefer.