What needs to do if there are two preferred suppliers offering the same product or service?

Benchmark the the two suppliers based on differents criteria price,delivery time,quality,certification,aftersales services,payment terms ect ect

Go for the vendor who give the best price through the best negotiation. 

Where there is more than one preferred supplier, quotation should be obtained from both. This allows a comparison to be made and ensuring the best value for money is achieved

There are a lot of things, like who will supply fast, how big is the supplier, what are the options if we have to change the product or give it back, their service ( for the product ) etc, 

Factors effecting supplier selection.

- Product technical requirements must be inline with project specifications.

- Price evaluation aginst both suppliers and project budget.

- Duration of delivery.

- Supplier Qualification and financial status.

- After sales services (maintenance, Warranty, etc.)

I will prefer the well known supplier and check for after sale services , after that i'll compare the price.

Negotiating the right deal with your suppliers doesn't necessarily mean getting what you want at the cheapest possible price.

You may want to negotiate other factors such as delivery times, payment terms or the quality of the goods.

in Such Case , it needs to Compare Other  aspects ofthe supplier proposal or offer

1-Suppliers Credits in the market

2 quality control certificates

2- Time of delivery and norm of prices

3-Aftersale services and warranties and the periods ,

4- Purchase Cash flow and payment terms.

5- inventory Prices

With evaluting the suppliers on above mentioned Parameters , The Choice is more convinient .

Identify product quality , Stock , Delivery schedule  apart from these cheque the prices also.

We need to know or understand about the service of the suppliers which is very very important specially in healthcare industry. As any moment you may have stock outs and you need sometimes more stock . Supplier should have the service to serve you in urgent situation

Check the background and credibility of the supplier.  Then decide which one is more reliable.