I would suggest to continue using this oil grade / viscosity, if engine health is perfect! Regarding brand, only Total Quartz 9000 Future series 5w-30! Its best for bucks!
Amsoil is better than Total, but at the same time, its premium and expensive.
I am personally of the opinion that buy reasonable priced good engine oils meeting all criteria, and replace them timely / early (like 5-7,000 Kms), and give new breath of life to engine (instead of buying expensive / premium oils, and dragging them for up to 10-15,000 Kms). Cost to benefit ratio may be same in both cases.
Engine flush is better and preferable, but if engine and especially its seals are weak, then it may be avoided.