Sharkis do have a great use of space. Which model depends on what you want to do and what you can find. As they are old boats now the condition and history is important. I would much rather have a nice Sharki than a poorly kept Maramu. But for carrying capacity, rough weather comfort and long distance sailing I would rather have the bigger one. For economy of maintenance and staying in marinas the smaller one has advantages, especially for just a couple.
The water tight bulkheads are very good. The same clever ideas are there on the different models.
Also, if only Amel were kind enough to still make a smaller boat ......