Curation is defined as 25% in STEEM terms but this is not always the case when converted to $ or SBD; it is mainly the SBD distribution that affects the true % going to curation, and since HF20 some also gets recycled into the reward pool.

As for a default setting, I personally would go with STEEM. I have set up my steemworld settings to STEEM to 4 decimal places. (Thanks to @steemchiller!) Indeed, steemworld is a good example of how flexible a UI can be, with data to suit most people, including EUR as well as USD.

One thing to be careful of is not to overload the data calls on long lists, such as trending or tag pages, so have one default for lists and perhaps more visible data, maybe in a popup, on a post page.

As a plug-in and overlay, @steem-plus can, I think, already be set up to show different prices.

One argument that continues unresolved is whether to use the blockchain price for STEEM or the market price average. IMO those algos that specifically use the official blockchain price should be duplicated as they are; to calculate a real USD value will, however, require market prices. Also, in my example, selling SBD for STEEM requires market prices, but a "conversion" must use the blockchain price.

This is just how I set up my data for my fund - what is important is how much STEEM I can earn because that I can manage, whereas the $ returns are beyond my control.