im building a new pc which one should i get 690 or the gtx titan
If you are going to spend $1000 on the video card I would go with the titan, it is a single GPU so you need not need to worry about games that are not optimized for SLI you get GPU boost (I think that is the name) 2.0 which will dynamically overclock based on the temps
What this guy said. Single GPU is always more optimized/stable than multi-GPU cards.
Titan is not as fast - unless you're goint to overclock the hell out of it - as the GTX690. But then you won't have any trouble with multi-GPU scaling, microstutter, and overall driver/game support.
http://www.overclockers.com/nvidia-gtx-titan-video-card-review
http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_Titan_SLI/
http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_Titan/
Read for yourself.