hmm just to clear things up by Native do you mean Native Instruments? They make a whole bunch of softsynths/samplers.
The main one used for synthesis is Reaktor which is their own modular synth which you can use to create other synths. They have a huge library downloadable/installed that covers such synths like Synthis, Roland Jupiters, Oberheims, Arp, Moogs and out there stuff as well. It can even be turned into a workable sampler or drum machine with certain synth presets.
You can also use Reaktor as a modular effect builder, you can create reverbs, delays, etc with it or download them as well in preset form. It's in my opinion more flexible in that aspect compared to Reason because of the way you can create your own synths/effects/samplers. It has a larger learning curve though if you want to get into creation of stuff yourself. Since you have to know a bit about mathematics and waveforms etc.
Native also makes Kontakt which is there huge sampler which can load almost any format out there and does it marvelously.
You get both of those plugins with Kore plus Massive which is a semi modular analog synth modeler, FM8 which is an FM (frequency modulated) synth which would cover all those 80s digital synth sounds, and Absynth which is their pad/ambient synth which is a bit more complex than Massive but mostly serves for good synth pads or long drawn out synth sounds. All in all a good rounded bundle.
Cons though is that all of those synths take up a lot more processing power than Reason does most of the time. If you want to use Massive and Reaktor at the same time or et al. you would have to have a computer that's up to snuff and an interface as well. Forget about running many tracks at once if you start to add them as plugins into your DAW.
Pros is that the plugs are very flexible and are now more intuitive in how you can control them and what sounds you can get. FM8 is infinitely easier to program than a DX7.
However imo Reason if you dig deep enough can create most of the sounds you get out of the virtual synth bundle Native has. The only part it's a little backwards is when you compare it to Reaktor since it's not a modular synthstation. If you like to mess with the signal flow lets say go from ADSR to LFO to Envelope to LFO again most of the time in Reason you can't dictate the flow. In Reaktor you can. This would matter to you if you're into a)mimicking some out there synth b) like to create your own synths c) are in a noise band
. Most people don't need to go that far into synthesis. Reason itself lets you still control signal flow with having each synth have it's own triggers that can work of a drum hit or of another instrument's sequencing.
Reason has it's own samplers which might be a bit flat imo since you have use either aif/wav files or their own formats. This means you lose a whole bunch of sample libraries out there. However the samplers they have which is NNXT and Dr Loop are very intuitive, you can set your own loop points and note ranges, and flow perfectly into audio schemes.
To put it short Reason because of the way it's structured makes it easier to route audio send sounds through inserts, effects, sequences than anything Native would do. Native has to use your own DAWs sequencing features and/or effects to let you have more control over the final sound. Reason doesn't because it has onboard controls and wiring schemes.
Rewire the audio interface Reason uses to speak with DAWs is very cool. If you have Logic you would see Reason outputs appear on it when you're using Reason as a slave. This allows you apply effects or bus stuff alot easier than with AUs which make you open more instances of the same plugin or do weird side-chainings to get the same functionality. The drawback of course would be that Reason can't be Rewired with every program or DAW out there which limits your choices later on. Likewise Reason is what you see is what you get which means if you don't like a certain synth sound or waveform for example you don't have a way to add more waveforms to alter the synth, or with the sampler if you wish you had some alternate way of adjusting a sample you only have certain parameters you can adjust. Big issue is that all the nice effects Reason has are only applied to the Reason interface so you can't send a guitar sound through Reason's Screamer effect and have it come out affected.
All in all if you want something that's not too taxing on your computer and very straightforward and professional sounding, if a bit limited in how you can use it, go with Reason. If you're into tweaking stuff, know your audio stuff pretty well and your computer can handle the processing and your wallet the hit, definitely go with the Native stuff it's worth it as well.