My DS was given the Baby Einstein one as a gift and we were lent a pastel shaded one. IME (and his) the Baby Einstein was so much better and we ended up rarely using the pastel one so it got put away. He loved the bright colours even from a very early age (just a few days old), and then as he got older loved bashing the toys, grabbing them, watching the musical star thing. The toys are a good mix as there are some soft ones, a rattle and some clanky disc things, plus a mirror and a picture frame that you can put any picture in. The star thing is great - it has lights and music, plus a smiley face which even tiny newborns love. And the green cushion is good for propping the baby and for tummy time. We've just put the bars away as he is now 6 months and sitting up, but we use the mat bit all the time, and the toys from it as well.
To be honest they are all pretty OK - the one thing I didn't think about was the washability of the mat, if you are thinking of one with a padded mat included. I was given a Mamas and Papas Lottie Ladybird for DD2 but she was a sicky baby, so the padded mat was pretty pointless as it was always covered with a blanket! It's "sponge clean only" which is a daft idea for a baby toy. I think the Tiny Love and ELC ones are washable.
Just a gym on its own is fine, as you can lay the baby on a blanket under it - all 3 of my DDs loved an old Fisher Price plastic one that I bought for DD1 15 years ago!
I was given a Tomy Winnie the Pooh one and it was hopeless. The toys were too high for DD to reach/see and it didn't really have any acticity ones.
Have now got a TinyLove one which is absolutely fantastic. Have also got two friends whose babies love theirs too. It is really well designed, has loads for them to look at, play with, touch and is washable. Brilliant!
We were given the first one for ds, don't know how much difference there is between them all to be honest but he still loves to play with all the animals from it at 21 months (the gym itself has been packed away). It is easily washable which is good as the music and light bit pulls out from the mat which can go in the washing machine. All the animals have been through the machione several times too and are fine