I made 2-3 orders from Boohoo. Depending on the clothing item, I usually wear small or sizes 4-6 US (UK 8-10). However, the dresses I got from Boohoo, I would personally go for size US 6 (UK 10).
Shipping was good. I'm from Montreal, Canada and my packages normally arrived within a week and if you order over $50 then you don't pay duties or shipping, which is pretty good!
I ordered from Missguided for the first time last week and received my order after 2 days. Depending on the clothing item, I wear size 4-6 US (8-10 UK). I'm also 5'3".
Shipping was very fast but if you're from Canada like I am, then be prepared to pay a lot of duties. I paid about $70!! I think that's what's stopping me from ordering from there again.
Discount Code: I also used 20% code NEWMG (It works on your first order).