Hello...not even sure if this is in the right place....

This is probably a stupid question but I'm working on Egyptian world in CAW and wondering what the best way to create a river is The Valley tool or Water planes?

Just using the seawater is easier. Water planes takes some getting right

Use valleys if you want a river at the same level as your ocean.

Use waterplanes if you want the rivers to have a water level above that of the ocean.

agreed with both answer above: the question implies your new with making a map with water... waterplanes should be used for lakes or rivers above ocean level but there are several things to get right for a good result.... The valley tool is way easier BUT if your handy: there are several good tutorials ->
http://www.modthesims.info/showthread.php?t=453392

Editing in a later stage can be difficult, with the valley tool you can do that without a thought...

With the assumption you're new to this I would suggest getting practice with the valley tool; Waterplanes are mostly used by more complex maps (which need practice on different fronts and attention to the valley tool; all raising and lowering for that matter) won't be a waste