To choose your pass I suggest you spend a bit of time considering your preference for travelling and budget.
If you are a free spirit who simply wants the freedom to hop on and off trains at will over both long and short distances on most days, then a 15 day continuous pass would be ideal (but costly).
If you prefer a small number of long hops to the next city or country then a 5 or 7 day pass would suffice (cheaper and can always be topped up with buying tickets for shorter journeys) but there is a relatively small premium for the 7 day pass.
You may find that the Black Friday sale is limited to longer passes so the 15 day continuous pass may be competitive. Remember that promotional passes are often not refundable or exchangeable.