Varnish recommendation: NONE - doesnt last long enough, lifts when water
intrudes underneath or through the wood.

Cetol: better to splash on root beer or brown paint with a straw broom
if you want a good looking finish in comparison to "cetol".

Consider using "Honey Teak" (www.signaturefinish.com)
Its a 2 part base coat and a 2 part top coat of polyurethane and
acrylic. It behaves and LOOKS like varnish.
Doesnt HIDE the wood nor is butt UGLY as Cetol ... or simple ugly like
Cetol Light.
On my present "teakey", the honey teak is now going into its fourth
season, and only with minor upkeep/topcoat. The longer its on the
lighter it gets. Can be flat sanded and hand-rubbed with rotten-stone to
be equivalent to the finest, most brilliant varnish jobs. (Hand rubbing
with rotten stone will develope a glass finish and the heat of hand
rubbing will develop a deeply irridescent 'patina' in the wood.) Its
recommended to apply a yearly quick top coat; but, some years I simply
power buff it with 2000 grit polishing compound. Typical sanding prior
to a quick top coat restoration is by using a 3M purple pad (100 grit).

The stuff is EXPENSIVE but in comparison to the short life of varnish or
the constant recoat of Cetol(which cracks/aligators severely when aged),
the stuff is a bargain when you calculate the cost vs. life of several
seasons (4+).
The manufacturer recommends 2 coats of base followed by two coats of
clear.... which you can apply in 1 or 2 days. I apply 3 of base and 4 of
clear - then I have enough to power buff the following seasons. If you
use it, lay on HEAVY coats with a soft 'artist' brush. At first the
stuff has a moderate amber hue; but, will quickly fade out to a 'honey'
clear in a few weeks. Use it ONLY on teak, not teak look-alikes such as
Iroko, etc.
Smith & Co. offers an equivalent called "5 year Clear" ... perhaps an
epoxy base material.

OIL: If you want a supreme OIL finish, dont use thin oil; but, consider
to use heavy 'resinated' oils such as NuTeak/Marykate .... and DONT wipe
it off between coats. Lay on several THICK coats, let cure a few weeks,
flat sand with 400 or 600 wet and dry, then add the final coat. Will be
equivalent to the brilliance of varnish. Will last 12-18 months before
it turns very dark due to UV .... then soak with trisodiumphosphate
(TSP) to remove and begin again. NOTHING beats the shine or brilliance
of hand rubbed (resinated) oil finish. I have a rifle stock that I did a
hand rubbed oil job on 35 years ago... it still looks like glassssssss.