Go for the most watts you can fit easily and preferably cheaply in the space you have.
If everything else is equal multiple smaller panels
will do better in the shaded conditions experienced on a boat.
2x 120w would give slightly more power than a single
240w panel, but the difference is small. A single
larger panel usually takes up a bit less space and is easier to mount than multiple smaller panels
of the same wattage.
In your example 2x140w (if that is not a typo) is better than 1x 240w. More watts and more panels.
Include the cost of installation
, with cheap solar panels
available this is more significant than ever. Delivery
costs can be much higher for the larger panels.