Ooooh, that's a big question for a Saturday morning and I am sure you will get many educated answers from Mumsnetters but I will tell you why I think breast is best.
My main reasons, very selfishly, are all about convenience - no sterilising, no formula to buy, no bottles that can be left behind, no worries about how to store made up bottles when you are out and about and how to get them heated, no stuff to lug with you when you go to stay anywhere.
I have experienced both sides, my first DS was exclusively b/fed for five weeks and then mix-fed until 16 weeks when he went onto bottles all the time. My DS2 had nothing else but breastmilk to drink (although also on solids from 17 wks) until he was almost seven months and he now takes a little water with his lunch and has never had formula, I find the situation much easier with DS2, I always have his milk supply with me, it is all ready mixed and ready to dispense whenever he requires it. With DS1 however I had all the hassle of bottles and for me (very disorganised person) it was too much.
There are of course many health benefits with b/feeding although I have met children who have been exclusively b/fed and still have eczema and asthma but I am sure the incidence of these things are greatly reduced. A b/fed child is also less likely to get gastric illnesses. There is also the benefit of b/milk being the milk human babies were intended to receive and therefor it is easier digested, there is less waste, often resulting in less dirty nappies (both my DS1 and 2 went through a phase where they only dirtied a nappy once a week) that don't smell so bad. Many of the benefits of b/feeding last the child throughout their life. There are also benefits to the mother, particularly from extended b/feeding, I understand this offers some protection against certain cancers.
I do personally believe that breast is best and worth any initial difficulties, although I do believe that women should be offered good help with b/feeding, although unfortunately this seems to be rarely the case. I also feel that b/feeding women have a responsibility in the promotion of b/feeding to feed in public and get people back to thinking of b/feeding as a natural and normal way to feed a baby.
mam, I am just curious, you do not say if you are pg, have a baby, are feeding, thinking of feeding, have fed. Are you trying to make up your mind?
As I said already others will have more detail for you, if Eulalia is out there she is a mine of b/feeding information and I am sure will post something for you. All the best.