Honestly speaking for myself I think roboto and Calibri are excellent fonts. Readable and aesthetically pleasing, what's the general opinion on these default fonts in the typography world?
They are excellent fonts. Neither is default across platforms though, nor are they serif fonts... For a sans serif, default font, I like Palatino. Classic, nice open counters.
I suggest that on any occasion when you're inclined to use Palatino for substantial quantities of text (as opposed to titles, posters, book covers, etc.) you would do better to use Aldus instead.
(Aldus is a companion face to Palatino; Zapf's intention was that Palatino is for "display" use -- titles, posters, etc. -- and Aldus is for body-text.)