The biggest determining factor should be the overall condition (floor, panels, etc.) of the two trailers you are considering - rather than the year. The "soft goods" (carpet, curtains, upholstery) are are easy fixes - no difference between years and you're probably going to want to update them regardless of which trailer you go with.
If the trailers are going to need restoration or "fixing", 1969 is a transition year so some things may be unique to 1969 trailers, thus more difficult to find if you need parts.
is the last year of the Corning windows - which can be difficult (or expensive) to replace unless you go with plexi/Lexan - however the rest of the trailer has more parts in common with the 1966
models, thus easier to find replacements if need be.
"Land Yacht" models were the basic trailers and "International" models had some upgrades - mostly in finishes & accessories. Neither are going to have gray water tanks, unless they have been retrofit by a PO.
Personally, I prefer the clean lines of the 1966-68 windows over the 1969 and newer framed windows, so it would be an easy choice for me.