Well, they're for completely different uses. If your car needs a jump start (which the PSX3 can provide), you should generally put it on a battery charger (such as the deltran) as soon as possible afterwards. Alternatively, driving on the highway for several hours should charge it up if your alternator is properly functioning.
The battery tender you mention is the type of thing you'd want to connect to your car battery if you intend to park a car and leave it for several weeks/months. Ex: if you have a car you only use in the summer, you should hook the battery to a tender in the off season or your battery might fail prematurely (ie fail to hold a charge). That particular model can also fully charge a dead battery, albeit slower than some battery chargers. The tender feature is always nice to have though.
A charger of some sort is always good to have. The jump starter is good for emergencies and might save you from waiting to flag down a stranger so you can use jumper cables, but it won't charge your battery.
Sounds like you made a good choice!