I would run conventional untill its broken in maybe 10k miles, Why? new engines need to have some wear so parts can settle/match, as a matter of fact the compression/power of unbroken new engines is smaller than properly broken in engines, afterwords synthetic would be my choice and with synthetic u could extend the oil changes longer.
Synthetics today are so good that tests have proven that a properly mainteined engine with synthetic oil may never need a rebuild as there is virtualy no wear on the parts.