I'm needing to pipe swirls on a bc wedding cake. Is it best to use bc to do this or RI? What are the pros and cons?

I have done this, and IMO always RI. (which in this case is just a stiffer buttercream)

I have come to realize there is RI and then there is RI.

I use meringue RI when I want to build things like boat, outline decos to fill with RI-flo, extremely hard flowers etc.

And when I am decorating on a cake(scrolls, any piping, flowers, etc) I use A buttercream RI, which is just a stiffer buttercream and crusts hard but edible.

you can look at my photos for examples. of each type.

tesso, what would a RI bc recipe look like? Is it actually called RI bc?

unfortunately I have not seen any specifics between what people call RI and what I term RI-buttercream. Usually I can tell by looking at a recipe which area it falls into in my book.

When I make a stiff bc for flowers, scrolls etc: It has no meringue powder, no cream of tartar.

When I make Hard RI it will have either of those in it.

When i am making RI for string work it will have a significant amount of cornsyrup to keep it from cumbling or breaking.

Like I said there are a lot of variations on RI. and usually they will have to be tweaked one way or another depending on humidy, heat, cold.

I suggest experimenting with some various recipes. And practice with them. That is how I made my extreme heat crusting bc recipes. . Make cupcakes, put all my different kinds of bc and RI and RI-bc on them and set them out in the sun for a few hours whatever wasnt a melted mess, or held its shape won.

I prefer buttercream. I rarely use royal icing for anything unless I need it to dry rock hard. For me, good ol' buttercream is easier, quicker, and less mess than mixing up another batch of something else!

I use BC for everything. borders, roses, flowers writing and even stringwork. I'm just not going to take the time to make 2 different kinds of icing when one will work just fine ('coz I'm basically a lazy person! ). I've never understood or seen a need for RI just to do some simple decorations on a cake.

Save yourself some time ..... use BC. It works great and tastes better.