Get a stable ski with adjustable length pedals. This is both the best ski to start with and is the most re-sellable. Chances are you will be faster on a stable ski than a wobbly one because you can get power out of each stroke without bracing all the time.
There must be hundreds of wobbly fixed length ski's cluttering garages around the globe. Don't make the mistake of thinking you will get used to a wobbly ski, you'll just get despondent about paddling, rather enjoy it from the start.
