We have both--and our daughter LOVED both. I got the Jumperoo for a shower gift and the exersaucer I found at a re-sale shop for $10! Our exersaucer she started to use around 3 months--basically when she could hold her head up well on her own. She LOVED it because she could see everything around her, and that kept her attention for quite awhile.
Then when she was about 5 months we got out the Jumperoo, she LOVED that even more than the Exersaucer, it was SOOO fun to watch her JUMP AND JUMP AND JUMP...really strengthened her legs.
So, with that I guess my recommendation is for either--both of them your child will love. If you have a second hand store near to you I would check that place out, it was nice having both-- I see Exersaucers there more often than the Jumperoos.
I would say my daughter used it until she could walk--so until about a year--then she didn't want to be trapped. Our daughter is small for her age (short) so she probably used it longer than most kids because she didn't physically outgrow it. Now she is 17months and stands next to them and plays with the toys--and even last night she wanted to get back into the exersaucer, and played for awhile...I think they are great investments!
Have fun!