this is where i have bought all my addis from http://stores.ebay.com/My-BestShop_W...eNameZl3QQtZkm
i have two sets of interchangeable boyes and i love them. i got the addis because boyes don't get as small as 16". I have 4 more pairs that i want that i can't find at a price i like and i will have all the circs i need.
i started using them because that is what the lady who taught me to knit handed me. she gave me bamboo. i don't use the bamboos much anymore now except with slippery yarn. i love the longer lengths when knitting flat because i have more control over the movement it seems. but i have gotten pretty use to the smaller lengths too so whatever is comfortable for you.
i have never used any straights but for the flex shaft needles from Clover. they are great too but like was mentioned before, when i get up i tend to lose them. when i drop a needle with my circs it is still connected to my work!