I think it's just a personal thing, I wouldn't judge someone or care how they chose to feed their baby, mom's have a hard enough time as it is!
I really wanted to breastfeed and when DS was born he had a tongue tie, the midwives encouraged me to continue to breastfeed though and his blood sugars were all coming back perfect! We were in hospital 3 days and I don't think he left my boob!
I knew all about cluster feeding and his nappies were fine (weeing and pooing) he was alert and not just sleeping constantly so i thought we were doing okay! But when we got home relatives convinced me he wasn't getting enough as he just wanted to be on my boob all the time, and I started supplementing. It is so hard for first time mom's the hormones, lack of sleep and pressure from everyone who has an opinion on how you feed your baby!
DS had his tongue tie cut at 10 days old and i managed to do a combination of formula, breastfeeds and expressed breast milk until DS was 6 weeks and then went to straight formula and I still feel immense guilt about this 15 months on 
I will never forgive myself for giving up and not trying harder because it was important to me to breastfeed, and I believe breastfeeding is the most natural thing and for me breast is best.
Other people don't share this view and think formula is best and that's fine too! My DS thrived on formula but I still can't stop the guilty feeling 
So if you think formula is best, brilliant! If you think breast is best, thats brilliant too! Just accept moms choice and support her and baby in any way you can 