Hi KeltoKel!
I think by 'activity center' you mean an exersaucer? I do have both. My dd loves the exersaucer (I have one upstairs and downstairs), but only for short periods of time. She is a very active baby and can't sit still for a second - not even while drinking her bottle or reading books before bed.
I have not yet used the jumperoo thing. I did bring it up from the basement last weekend, but we really don't have door jams to hang it from that leave enough room for jumping. And I certainly don't want to hang it in the bathroom's door jam. So I haven't used it yet. And I'm not sure that I will. I got it as a baby shower gift, so it's not like I spent money on it myself.
Also, and this is probably just me being paranoid, but my SIL had a stationary jumper and used to put her dd in it all the time. And with jumping her dd would always stand on her tippie toes and push off. So when it came time for her to walk, she'd do it on her tippie toes, hanging on to stuff. She was 15 months before she started to walk normal!!!
My dd loves to stand and pull herself up on things - flat footed. I don't want to screw that up! I know, I know, I'm being paranoid!
Anyway, the one exersaucer I have has these legs that you can pull down to make it stationary. Or you can put them up to make it 'bouncy'.
I guess if I were you, I'd really look to make sure you have a safe door jam to hang it from before buying anything.