Midi Keyboard or Keyboard Synthesizer

Hello,
 
I have recently upgraded my Sonor to X1 Studio. I want to record some songs they will be standard rock and pop songs with recorded guitar, vocal and drum tracks (recorded individually by microphone by me). I want to be able to add some synth sounds as well as recording some basslines and horns with the synth/keyboard. I have used an earlier version of Sonor to record a few songs and I used a cheap yamaha keyboard for midi but the voices on it were poor and I was unhappy with the results.
 
I'm not sure what the Sonor X1 Studio built in softsynth sounds are like so I am looking for some advice. Should I go and buy a midi keyboard to use with the soft synths within the software or should I go and invest in a keyboard synth? Any recommendations? Obviously the midi keyboard is cheaper but the Keyboard synth offers betters options for playing live and jamming with other musicians (which may also happen seperate to recording).
 
I have a little experience with midi and keyboards but not enough to make an informed purchase.
 
Many thanks

You might consider the M-Audio Venom synth ~
It's being discontinued by M-Audio (probably due to company mergers more than anything else), but by all accounts it's a VERY capable VA Synth, audio interface, and MIDI controller (DIN and USB), all in one.

Sweetwater had a blow-out for $199 (cheaper than most comparable MIDI-only controllers!) but they sold out pretty quick.  You might check with some of the other big online music retailers and see if anyone has them available and might be willing to do some price matching.

As far as dedicated controllers go, I really like my Novation Impulse 49!
Once you get your head around Novation's Automap (which really isn't that difficult), it works quite well with Sonar.

The biggest drawback - it MUST be powered over USB, so if using it without a computer (it has MIDI DIN connections), you need to use a small USB power supply to give it some juice.

The synths inside Sonar are certainly good enough to make great sounding music so a controller is not a bad option. But also the concept of getting a synth is also a good one too especially if you are going to do any live gigs etc..You can also use Sonar to address the synth engine inside the synth and use the synth to generate a lot of the music too and that in conjunction with the VST's in Sonar might prove to be a great combination.

What sort of budget do you have in mind for the synth. I would choose a more useful and overall meat and potatoes synth that can do a lot of things well rather than a more specialised thing like Venom. eg Korg Kronos. (Why not get the best hardware synth in the world right now and be done with it) What synth you can buy I guess does depend a lot on what sort of money you have available for it.

If I bought a fully fledged synth I dont mind paying $300-600 however if I was buying a controller I would expect to pay a lot less.

If you have been disappointed with synth sounds from any source, you may find more disappointment in that price range for a hardware synth. There are quite a few serviceable free (or quite cheap) softsynths available.  It is even possible to find some usable samples and romplers for cheap if that is what you mean by a synth. So on a purely sound per dollar investment, that would be the way to go. 

Likewise with a keyboard controller. I am a terrible keyboard player, but even I am pretty put off by the spongy inconsistent response of the inexpensive controllers I have used. Good ones cost a fair amount of money.