I have been using Cetol on my teak for a few years now, and am happy with it. Cetol has come a long way from the awful orange-colored product they initially sold - a product on which many still judge the company. A guy a few boats down from me last year somehow got an old can of Cetol (cheap) - yuck - after the first coat, realized his mistake and had to start again!
My process: Having cleaned, repaired and bleached the wood (to remove stains), I put on a couple of layers of Cetol Teak, and then 3 layers of Cetol Clear. I now touch up any dings during the year (important!), and then recoat all the brightwork with Cetol Clear every season (a relatively quick and easy job; just clean with a kitchen scouring pad and recoat). I said important above because if you don't touch up a ding quickly, water/weather will change the color of the wood under the ding, and it will stay a slightly different color.
Cetol Advantages: Very easy to apply, very easy to maintain.
Disadvantage: Not quite as nice as varnish (maybe 80% as good for 20% the effort...)
Varnish:
Advantage: Beautiful
Disadvantage: Difficult and time-consuming to apply. Generally needs to be reapplied twice a year (a couple of layers, sanding between each layer). Less forgiving/more fragile.
I have varnish below, Cetol topsides.....