To prevent this from becoming a one sided, let's examine the pro's and con's of each option.
Reaktor sessions:
pro) Many more plugins available for download then one will find *initially* for pluggo.
pro) Reaktor has a deep community that will continue this trend.
cons) No matter what, you can't edit the patches (and buying the full reaktor seems a redundency, you'll get a replacement not an expansion of service).
cons) Bloatware - I tried using some reaktor 4 demo patches in live, and they quickly blew my cpu meter bar out of the water. If you could edit the patches, you could at LEAST turn off some of the useless visuals.
cons) Pc-Centric company that can't seem to make stable software for mac (historically and currently, regarding reaktor till 4.0.4, intakt, sessions, kompakt, etc).
cons) In relation to pluggo, instances can't reference each other (i.e. patches can't cross modulate).
cons) Insane copy-protection according to a krv-vst.com review (CD AND challenge/response at every startup).
cons) Fewer effex plugins out of the box (made up for by access to the user libraries).
From kvr-vst
The lib installed from CD (probably the same shipped with Reaktor 4) includes 9 synthesizers, 4 sequenced synths, 4 samplers/transformers, 2 live tools and 9 effects. I do some of them like more, some less, but now I'm not restricted to a limited small selection. You now have access to a huge collection of Reaktor ensembles from others and the NI page. Besides the "Premium Lib", shipped with Dynamo and Reaktor 2, and those new with Reaktor 3, you can find as a registered user currently over 1300 user contribs for download there.
Pluggo:
Pros) Mac-Centric Company (
www.cycling74.com).
Pros) Patches CAN cross modulate.
Pros) More pluggos out of the box.
Pros) Pluggos made by others can be added to your bundle, and acquired for free (potentially).
Pros) IF you eventually decide to become a programmer, you can purchase max-msp and not reiterate any of your current ability (i.e. pluggo expands max if you have it, and still rocks if you don't).
Pro) It has yet to be seen how they run on X, but the interfaces for the pluggos tend to be FAR less cpu intensive then Reaktor, so you should be able to load more into a set (this is also assuming their code works efficiently, and that the runtime enviroment/shell doesn't muck things up a bit).
cons) Far less pluggos available on the net due to a) the higher difficulty of max-msp (smaller community) and b) it doesn't exist yet... yet.
cons) Pluggo were well known to behave oddly in certain hosts, Live being one of them ironically (see the Pluggo tutorial on this site). This may, but probably won't, be an issue today with xpluggo.