Agree with Loopy that if you BF, you'll be more mobile while out and about if you use a sling. My own experience was:
Sling that you can bf in = BF while I walk, baby drifts off to sleep, am relatively free to do things, such as continue my walk.
Pushchair = constantly having to stop, sit down somewhere, bf baby for potentially a long time until she sleeps, then hope she doesn't wake up as I put her back in the pram - and if/when she does, start all over again.
One thing I forgot to say is that regardless of whether you use a sling or a stroller, you need to set yourself up with certain paraphernalia.
Stroller:
Comes with big tray for all your stuff, handles for hanging bag from, and may have to buy a stroller net.
Clear pull-over raincover for stroller, raincoat for parent.
Sunhat for parent, sunshade for stroller/hat for baby.
Warm coat for parent, cosytoes/jacket/snowsuit for baby.
Slings:
Good rucksack for when your baby is small, a changing mat that has incorporated pockets (such as oioi, but we have a cheaper one that I can't remember the name of)
Choose between messenger bag, backpack that attaches to sling, or shopping trolley, for when you carry your baby on your back.
We did carry our baby in the sling and push our things in a stroller, but found it more awkward to manage than a rucksack or trolley (although a stroller does hold more!)
A big umbrella for both of you, or one of the specialist babywearing raincoats on the market (that cover both of you) or you each wear your own raincoat or a specialist rain cover for the sling (such as Wilkinet) and you have your own raincoat or umbrella
Babywearing coat or poncho for both of you (can DIY) or a warm sling cover for the baby and you wear your own coat, or dress baby in warm clothes
Sunhats/UV-blocking sling cover/parasol
Many of these things can be bought second-hand and re-sold without losing too much value (depending on how much wear and tear and what the market's doing)
Sorry if this is waffley but I guess you get the picture - you have to equip yourself equally heavily, but quite differently, for a journey by either sling or stroller.
We struggled to get by with all-day outings with a sling because we only had the equipment for stroller use. If we have another baby, we'll be set up for it and probably won't bother with a pushchair at all.
Having said that, if I could go back in time and money and storage room were no object, and I had no idea whether my DD would take better to the sling or the stroller, then I'd equip myself thorougly for both
Oh and try here - check out the common questions secition
Anyway, good luck, and let us know which sling(s) you get!