I've been wearing Uggs since way before they were fashionable, maybe 30 years?  Back in the day they came only in the basic style in a tan color but I wouldn't be without 'em.  Now that the rest of the world has caught up with me, I get to choose from a rainbow of colors and several styles.  What larks!  The basic boot is still my favorite.  This time I chose grey.  It's lovely, neutral but without being too dark for winter.

I love Uggs because they are ever so warm even without socks.  In fact it's preferable to wear them without socks.  The lanolin in the sheepskin is very kind to the feet.  I've tried cheaper imitators and they don't seem to have the same quality of wool or the same quality construction.  It's worth it to stick with the originals, especially considering how long they last.

A few observations that may be helpful to readers:

1.  There is no arch support.  If you have high arches you may want to allow for some sort of orthotic to make all day walking feel good.  I like the kind that strap to my arch so that I can just slip into the boot.
2. Related to this, if you have very high insteps it may take some time to ease on the classic boot.  It has no zipper and is purposely snug in that area to offer some support.  I find that the classic Ugg quickly eases up enough for me, but my sister for instance can't get 'em to be comfortable.  I'd say if the fit over the instep is painfully snug, think twice.  The low Baileys and some of the knit boots might work out better for you.
3.  Ugg tells you to round down rather than up but that's not always true.  I'm a 7 1/2 but do better with a size 8 boot than a 7.

These three things add up to one piece of advice:  Good idea to try your style for size the first time either by buying both sizes and returning those that don't fit or by trying in a store then returning to Amazon for the best price and a full color selection, which few stores carry.  The good news is that my size has remained constant all these years.  Ugg clearly keeps their sizing consistent.  So you should only have to fit once per style.

Finally while the classic Ugg boots are somewhat snow weather resistant the soles don't have optimal traction and the boots can leak in a very unpleasant way if one doesn't spray periodically with silicone, especially at the seams to the sole.  If it's very wet and/or very slippery, I wear snow boots.  Ugg makes snow boots now in case you're brand loyal.