Firstly, before you decide whether to proceed with a resale HDB or an EC, you need to know your own objectives.
Ask yourself these few questions:
How do you see yourself in 5 years time?
How will a HDB flat or an EC help you in archiving your objectives?
What is your next step going forward after the 5 years?
Only by asking yourself these questions then can you be clear on your decision making.
After you're clear on this, then you can proceed to source out the best possible outcome to your decision, and look into the finer details of things.
As for my opinion on outlook in terms of price for a development near a site with multiple ECs being clustered together, I would ask you to imagine yourself to be a BUYER of such a unit in 5 years time.
Again, ask yourself these question:
If condo A, B and C are just next to each other, with the prices comparable, what choices do I have? Will I have ample choices to choose from?
Should you need help in making decision, feel free to call me for a discussion. I will be glad to assist. I can be reached at 97486305