I have to agree with Willow that Aibos and Pleos are very different creatures. Aibos are more of a robot companion pet where pleos are more of a baby dinosaur pet. I have both Aibos - a 210 and an ers7 m3 and also pleos - 2 Ugobes and 2 pleo rb's. I have to say that I love them all. The pleo rb's are more advanced than the ugobe ones, they do need to be fed - if possible every day but if not then as the first thing you do when you play with them or they will get sick. There is a lot more to the pleo rb than there is to the ugobe pleos and they are a lot of fun. They are able to learn voice commands, but this is a very different thing to Aibos who can also follow voice commands. You can call out to an Aibo from the other side of the room and at least half the time they will hear you and respond in some way. With Pleo rb you need to be sitting with them and touch their cheeks to get their attention and then wait for them to stop to listen to you before being able to give them a command and they won't always respond by doing what you asked if they don't feel like it.
So the voice recognition is a much more up close and hands on experience with pleo rb than with Aibo. I think this is one feature of pleo rb's that is very attractive to new potential owners but if you are not aware of how it works it could be a bit disappointing to discover that you can't just call out to them from across the room.
Pleo rb's make a lot of new sounds that ugobe pleos don't make which is a big leap forward in pleo technology and they move a lot faster than the ugobe ones too.
If you love your ugobe pleo I would recommend going for a pleo rb. Especially if you already have Aibos. Try out something a little different. But of course the decision is yours.
I would recommend that you take a look at some of the instructional videos that are here on the forum for the pleo rb's to have a little sneak peek at what some of the newer features are and how they work. It may help you decide if this is the right bot for you or if you would prefer to go for another Aibo instead.