I completed B.Tech in civil engineering but want to do PG, which one is better: M.Tech or MBA?

If you have got good command over trade in which you have pursued engineering which is civil, then it will be beneficial to purse M.Tech in Civil. Otherwise, go for MBA.

It depends on your area of interest. If you are interested in business or management orientation go with MBA. But, if you want to pursue or master a particular specialization, which you tend to do, go for M.Tech. Just make a clear decision about it as both are beneficial in terms if job aspects. You

This would depend on your interest areas and career aspirations. In case you intend to pursue a career in Technical / research / academics area then M.Tech/MS is better. However, if you want to move into general management the MBA is better.