Regarding Migrating data from Legacy to SAP

Hi All,

We are in Migration Project. We have to upload data from legacy to SAP, either using BDC or Cross-Applications in the following SD scenario's.

1. Customer Master

2. Inquiries

3. Quotations

4. Proposals

5. Sales Order

6. Goods Issue

I would like to know, which concept is better for each of the above scenario. Each option have advantages and disadvantages. So, I need suggestion regarding this.

Regards,

Sathya.