Age spots or sun spots (medical term: lentigo, plural lentigines) are collections of melanocytes in the upper layers of the skin. They typically occur in sun-exposed areas such as the neck and chest, where sunscreen use is less common, but can also be seen on the face or other areas of the body.
The best laser for treatment of these brown spots is one whose emitted energy wavelength (color) is best absorbed by melanin (the pigment in melanocytes that gives our skin its coloration, and which darkens with ultraviolet exposure). Melanin absorbs energy best at the blue-green end of the visible light spectrum, with less absorption at the red-yellow end of the spectrum, so a laser which emits energy at that wavelength (color) will have more energy absorbed by the pigmented spots. Enough energy selectively-absorbed can lighten or remove the pigmented spot, with less absorption and damage by the adjacent normal skin that could cause a burn or scar. That's how it works. So which laser is best?
Let's pause for a second and discuss IPL or BBL. IPL (intense pulsed light) or BBL (broadband light) are essentially big, bright lightbulbs (flashlamps) that emit light energy across the entire visible spectrum, not just specific wavelengths or colors, but white light of all wavelengths through a handpiece to the target, your skin. Since the pigmented spots absorb energy at part of the visible spectrum (the blue-green end), of course these broadband, full-spectrum, white-light sources contain (some) energy that can be absorbed by the pigmented spots. And lots of wavelengths that are not absorbed, but still heat the skin. These devices do indeed work, but lack the selectivity and specificity of a single-wavelength laser.
Since IPL or BBL include a lot of "wasted" energy in the remainder of the non-absorbed light emitted by the flashlamp, that energy goes somewhere, and that "somewhere" is your skin in the form of thermal energy (heat). Which is why you can have burns and scars from over-aggressive power settings when these devices are used for sunspot removal. Properly used by experienced operators, IPL or BBL is "just fine" and can indeed lighten or remove your spots. However, neither is a laser, and neither is "best!"
But, a green-light laser is better! The KTP laser emits energy at a green (532nm) wavelength that is much more specific and selective for brown spots, with that color of energy being more effectively absorbed by your spots, and less by your skin! KTP is not a brand name, but stands for the crystal (Potassium--K, Titanyl--T, Phosphate--P) that actually frequency doubles (wavelength halves) a 1064nm Neodymium:YAG near-infrared laser to the desired 532nm green wavelength that is best for pigmented spots. Since oxygenated hemoglobin has an absorption peak near 532nm, tiny blood vessels (telangiectasias and angiomas) are also best treated by this (KTP) laser.
So, you shouldn't use the laser your doctor owns, but use the laser that is best for the job at hand. If that means finding a different provider who owns this laser, so be it. But when there is indeed a laser that is specifically engineered and designed for specific purposes, that is the laser to use--even if there are other devices that do the job (not as well). A hot poker gets rid of brown spots too, but you certainly don't want to have that device used just because it is what the doctor "happens to have on hand!"
Resurfacing lasers are not advised for the neck or chest skin as there is too high a risk for scarring. Even fractional lasers are used for skin removal, and are not specific for brown spot treatment. We own both CO2 and Erbium:YAG resurfacing lasers and use neither for brown spots!
For full disclosure, yes, I do own a KTP laser (have used it for over 20 years for exactly these indications with splendid results.) But my partner and I own 5 lasers, and lease several more for individual uses, each specifically-designed for the application at hand, not a "1-device fits all" approach. Too many lasers are sold to physicians as "this one does it all!" devices. Nothing is further from the truth, but too many doctors do not have training in the biophysics of lasers.
If there was a high-energy short pulse-duration argon laser (488 and 514nm), this would be as good or even better, but this laser does not exist commercially. So, KTP is indeed the "best" laser for your spots. Good luck and best wishes!