SQLite has many more features. It has more types, more functions, more SQL support. It also requires significantly more resources; they claim 100KiB of heap space and 4KiB of stack space with at least 300KiB of compiled code, stripped as small as possible. I don't know what this means.

LittleD gives you the bare basics, using well under 100K of compiled code, and under 1K of RAM for average queries, period. You will soon be able to strip out the query translator and "precompile" your queries with parameters to bring the total compiled code down to under 35K on device. This is not always desirable, but in some cases can be very useful.