My two plots run from North to South, at the moment I have always planted across the slope west to east so that I can catch the rain , would it be better to plant the other way so that the rows get a full days sun?
In theory, yes
BUT
I runs my beds east to west too :)
The first year I sowed religiously in faffy short 1m rows north to south, but this year I have easier, long rows, east to west.
For most crops, the s'wards rows matured slightly earlier, and the n'wards ones slightly later - effortless succession and longer cropping :D Others like onions and leeks are planted in blocks, so it doesn't matter which way they are facing.
I made a mistake planting tall PSB half way up the plot last year, and rows of overwintering broadies to their north - the beans all suffered from lack of light and few survived the winter :'( Now the firm rule is to sow and plant tall crops in the north, short ones in the south. I bet any landscape gardener would know that :-[
It sounds like it's sensible to run your rows like you do, across the slope. That way they all get comparable soil conditions and rain. That's what most civilisations faced with a slope have done - all those Mayan/Japanese terraces :o
If you're keen to experiment, you could try a little patch? I have this year, and it seems to make no difference to the quality or yield, so I'm sticking to my (east to west) layout ;)
Mostly it doesn't matter, the only things you have to watch out for are tall crops like runner beans that can shade the shorter ones.
which can of course be used tro benefit, i.e. plant spinach and lettuce in their shade.
i would also plant across the slope in your condititions. it is more important im my opinion to keep the soil stable and catch the rain.