I want to start this off saying this is nothing more than my mere opinion and *a lot* of any robotic-type pet has to do with the owner and their perception/interaction/personal tastes so you always have to take that into consideration.
I have owned both a 2009/10 Innvo Pleo (an "older" model - but post-Ugobe with some improvements) and a Pleo RB. I'll start by saying that after personal reflection I preferred the Pleo over the Pleo RB. And would actually consider buying one again. And here's why...
For me, the Pleo RB while being more pet like in terms of needs, I found it too needy - and too hard to tell what was going on sometimes without assistance from ProbeRB (a little tool on an SD card that helps read out/alter data on the RB). I found the feeding requirements way too repetitive and frequently required. If I don't have time to play with the RB, I don't want to turn him on and have the first thing I do be feed it 2-6 times in a row. Further, I think all of the accessory packs are (and this may be cynical) just a way to get more money out of the Pleos (which I support anything a company needs to do to be profitable, so this is not an insult). A few minor part of the learning stones were already in the regular Pleo, and I don't like having to pay extra for some lackluster accessories. For instance, I really enjoyed the death skit and the laugh under the "Play" (or whatever is the real title) stone. However, you have to make Pleo RBs listen to you first. This involves either clapping (in relatively close range) or touching the the cheeks and waiting for it to listen to you. This is the extent of its voice recognition. If it could hear/listen all of the time or repeat/do tricks on its own, I'd say this adds to its pet-like quality. However, the interaction it requires from the user takes away from that pet like quality in my opinion.
Now, I do like the RB's mechanical aspects better. It moved relatively faster than my Pleo (though I think the Innvo models still ran faster than the Ugobes). It also had more "lifelike" movements such as curling a bit when you pet it.
However, I liked my Innvo Pleo much more - and if I had known I would have went "bust" on the RB so quickly (mind you I have a short attention span), I would have kept it. The older models (including Ugobe) run the same software. I found this one much more cute, and while more repetitive, it felt like it had more of a soul vs. being a nagging robot with ehh input from a user. However, this just goes for my personality and personal taste as stated above. Every Pleo-owning user here probably has a different perception and relates to their Pleo in different ways.
I also own 3 AIBOs (ERS7, 210, and 111). For my own reasons and tastes, these are all much more pet-like. However, the one I'd probably recommend is the one you ruled out for pricing reasons (VERY understandable - I shied away from AIBOs for awhile until my membership here naturally led me down that path lol). These fit my personality more and provide me with exactly what I'm looking for. They also seem more pet-like to me though their form is clearly robotic - so it's not so much as good as a pet as it is as having a robot pet - whereas I find Pleos more of a robot imitating a pet instead of feeling like a robot pet.
And you will definitely get used to the "noise" - I swear it comes out more pronounced in videos than it is in person but maybe that's just because it simply seemed like background noise to tune out after the first few minutes of running it.