Which is better: Smartskin CO2 laser or Vivace?

lasers do not tighten skin and microneedling RF treatments need every 1-2 months to keep skin tighter and improved. 
As we age the skin sags there is  nothing  you can do that but try preventative  energy-based or thread-based  treatments or get a neck/facelift earlier in the aging process.  There are numerous options and some can be used in combination to get best outcomes but you need a consultation with an expert.
Options include for skin tightening :
thermage radiofrequency to heat skin and tighten it over time and prevent the aging process
ultherapy highintensity ultrasound to contract muscle and tighten the face and neck and prevent the aging process
PDO nova threads or instalift threads for immediate lifting without surgery and long term collagen production
sculptra injections for collagen production to areas of the face and neck with crepe skin or early sagging
btl exilis ultra, venus legacy, thermi250 , or inmode forma/contoura  for constant collagen stimulation monthly with facials
facelift/necklift with fat grafting/fillers if you need a big improvement
ThermiRF or J plasma /Renuvion or Inmode FaceTite   internal heating and tightening to long term internal heating and tighting with or without surgery
Platysmaplasty to tighten the muscles of the neck long term and create contour
Facial implants or fillers to contour the jawline and chin to improve the apperance of the nec k
Fractora/Morphenus8 or Intensif microneedling RF for improve superficial tightening, neck and chest wrinkling and crepe skin 
You need to see an expert in facial sculpting and age prevention.  Best, Dr. Emer.

Thanks for your question. It seems like almost every manufacturer has the new RF microneedling device that is "better" than the rest.  We offer over a dozen different energy treatments including fractional Co2 laser.  We do not have an RF microneedling system.We have recently evaluated 2 different RF microneedling systems.  We found it was MUCH more painful than what was promised.  The downtime was 10 to 14 days.  The results do not appear to be better than other devices with less discomfort and downtime.  We won't be buying an RF microneedling system any time soon.  I hope this helps.