I prefer to oil teak. If it has been varnished, sand it all off, get some 2 stage teak cleaner to clean it , then simply wipe it down with teak oil. You'll never have to sand again, just wipe it down with an oiled rag once a month or so. If you let it go too long and it turns grey again, just hit with the cleaner, and oil again. Varnish is just too high maintenance.
With varnish, you should always sand it before re-applying, and the punishment of a Laser tiller is sure to crack and chip your varnished finish. Then you'll have to sand it all off again to get it to look real good. Varnish does not repair well. With oil, you'll never see a ding in the finish.