What kind of oil?

I have a 2000 4cyl camry with 178,000 mi.  Two
weeks ago I took my car to the dealership to have
the oil changed, fuel topped off, check the brakes
and just get it ready for winter.   I live in Chicago
and work in Peoria and rely heavily on my baby.  
Just last night on my way back home my oil light
kept going on and off.  Luckily I was just a few
blocks from the house.  When I checked the oil the
only thing that was on the dipstick
was"LITERALLY" on the very end tip!  Not even
meet any markers on the dipstick!  The
serviceman(that I've known since I've had my car)
said everything was fixed but just do not wait so
long to change the old since my car is considered
old now.  He said that he did see some leaking and
that will be taken care of.  That being said I haven't
seen any leaks where I park at work but I can't tell
when I get home in Peoria because its dark when I
leave for work and when I get back home.  My
question at the moment is...  I've been searching
the internet like a maniac for this question and
EVERYONE has THEIR OWN take on things which
makes it a little confusing!  Simply put my question
is...  In the winter which oil should I use for my
2000 camry at this time the 5W 20 or the 5W 30? I
know the 5W 30 is recommended but I normally
take my car in to be winterized and I should have
asked but I never had any issues with my baby
since I've had her till now and never asked what
type of oil they used when they winterized it.