Like anything, there's more expensive and cheaper products and the better quality you can expect from spending more money in most cases. I have found that more expensive teak oils last longer, but oil is subject to evaporation and so has to be reapplied to stay nice.
Varnish is more of a labor of love and following the manufacture's recommendation is recommended for best results. Teak has natural oils and so that can be a problem with some varnishes for good adhesion. Epifanes has a varnish formulated for teak that I recommend. But, varnish is slippery unlike oiled teak, especially when wet. So, a rubbed effect or satin varnish might give you more grip under foot. Varnish has UV inhibitors in them, but they are not for ever protection. The last only so long, so reapplying coats of varnish replenishes the UV protection.