Either sounds good as long as the "other" building of the
2 doesn't block out sunlight in winter.
Southwest would be warmer later in the day,may stay warmer late in the
day but possibly cooler in the morning when it''s coldest.

I agree with Jim. Southern exposure might work better to warm things up more quickly on your "coldest" mornings.

Thats what I was thinking too. The south west facing wall does not get the morning sun to melt any frost that might have came. It does get a fair ammount of sun later in the day. However being near the two buildings I thought that it should hold heat longer. It also is surrounded by rocks, so maybe that can help make up for the lack of morning sun. I havn't had too many chances to see if frost is a problem there but I know I seen frost when I parked a car there. Cars always get colder than the surrounding air temps though. I seen frost on cars at 35f.

The only reason I didnt suggest the south east side is because it is also in-between two buildings, so it wont get the morning sun or much sun at all during winter.

The south facing wall does work fairly well for me,I just think it needs a protective canopy, and rocks around it instead of the bark I have. I have seen a few of my bananas stay green the whole winter there multiple winters, but only the ones close enough to the wall where the over-hang creates a small artificial protective canopy. The ones that have out grown it get fried every year but it usually takes 2 or more frosts.

It seems to me that with a protective canopy I can keep temps up by at least 4 degrees. Even at our coldest morning this year at 28f, no frost under the canopy. I dont know when it stops becoming frost free, but 22f is a good bet. That was the coldest I ever seen and it did fry all the bananas. Usually winter is mild and stays z9b. A coconut palm I planted there stayed alive until mid/late Jan. Almost made it into spring. It dies just as we were getting 70fs in the forecast. :( Yet the week before it died we had the coldest week of the year but not coldest nights. It got foggy and temps barely reached the 40f's during the day, but at least the nights only got about 3 degrees colder at the most. It was after that it looked sick and started to shut down.

I would stick to the south side and give it winter protection and Christmas lights on cold nights.
The southwest wall may or may not be better depending on hard to measure factors. Does cold air arrive on westery winds in your area. The other walls will be good frost protection, but west winds can be cold and if the walls block a low winter sun.. its too cold, too often, too long. Why not plant boths sites and see which works best.

It really depends...some z10 palms DONT want hot reflected summer heat. Others,wont take the valley's upper 20's.
For you,something very marginal would be Triangle and Majesty or King palms...but realistic chances they would survive or thrive.
I would skip time on coconut and go with Parajubea..some like that valley heat,and they have very coconut like fronds.
Chances are if you go any of those palms-you'll be the only one in the city who is!

Do a little experiment and place some (a)remote sensor(s)
in both areas,maybe it will help you find out if the 2 building
area is actually a better micro-climate or at least any
warmer.

Might be worth a try.

I am not sure witch side wind comes from but I believe its usually a southernly wind.

There are many majesty palms here,very few king palms, and I dont think I have ever seen a triangle palm here. I think it would be interesting to have palms that you dont see alot here, washy's, date palms, queens etc are very common.

However nothing can cure the lure of the coconut! lol! They sure do look so nice in summer here, and grow so well. Even above 110f with low humidity they grow fine. I know I will never get one to survive winter outside here with no help, but it would be nice to have a thriving coconut palm that you might one day get a fresh coconut from. I thought it would be cool to have one that does get some protection but isnt in a green house. Something simple and easy like plastic. And maybe with the right micro-climate it could keep it warm enough during the day to do some growth, even slow growth would be enough to keep it through a winter. As well as keeping the night time temps up as well, and away from 32f or below.

But A frost cloth strung with christmas lights work fine on frosty nights. A green house with a heater is always going to be tempting, but besides the cost, it would eventually need to planted inside it. If your in California, that ruins the fun. Yes, alot of challenges lay before me, and it proabaly wont work. But thats the fun part, it is trying to do something others havn't.Probably a very good idea is to plant higher up, possibly in a raised bed. All sandy soil too, with plastic on top to keep root zone dry. All this might do is delay its death, but maybe I could get lucky and pull off 1 lucky year. That would be worth it.

I do need to find a few high and low recorders to keep a track of temps in each spot over the next few winters. Problem is most wont read temps below 32f.

Thanks everyone for the reply and advice :)