I think this one will have to be a tie, I simply don’t know which I prefer more. Neither is a magic weapon or armour, though there are some really cool ones out there (a Frost Greatsword springs to mind, lol). I do like in 3.5 edition how variable you can make magical weapons and armour, and it really bugs me that 4th edition took all the customisation out of them. They even took away ability boosting items! Who would do such a thing? 3.5 edition had so much more in terms of magical items.
Anyway, moving on. From 3.5 edition then, my two favourite magic items are as follows:
1) Bag of Holding: Of course. It’s a bag that can hold lots of things! What’s not to like? By far the most useful item ever, particularly due to the infamous Portal Bomb idea – where the combination of two extradimensional devices cause rather nasty results. Actually, I’ve just found a very interestingthread on this point, though apparently it isn’t as devasatating as I had previously thought. Regardless, Bag of Holding is the item for everyone, especially the wizard with no strength to speak of, or the rogue who really wants to get away with a LOT of loot.
2) Ring of Sustenance. It’s cheap, it takes a week or something silly to acclimatise to you, but once it does you never have to worry about poisons, finding an 8 hour breathing space mid-dungeon, night ambushes, or your party members stealing your things ever again. For 2,500 gp, this handy ring provides you with nourishment forever, so you never have to eat or drink again. It also lets you rest faster, so that you only need 2 hours sleep instead of 8. In theory, this means that wizards can rest and then prepare spells 3 times in a single night, which can be very useful. It’s also the other item which I would love in real life, not because I don’t enjoy sleep or eating, but because when things got really chaotic, I would have hours more time to do it in. Wonderful.