im looking to buy korg triton..
but i see there is old triton, the newer korg taktile with same sounds and also korg triton rack

what should i seriously get? help

 

I had Korg Triton Pro either 76 or 88 key (I can't remember which) and loved the touchscreen on it but not sure if the others you mention have that option and it was pretty big too so might be something worth taking into consideration. It has some great sounds and love the Super Sweeper/Sweeper Strings Presets and many more.
Triton and Triton Extreme also available on sister site as VSTi (instruments) also by Korg themselves.
The TRITON Extreme is the most powerful model in the series, featuring the first-ever "Valve Force" vacuum tubes in a music workstation, and most of the new PCM and EXB-PCM series waveforms. The powerful, analog-like sound of vacuum tubes can be used with software for incredible sonic performance