BGP preference to a preferred path

Hi fellow networkers :-)

I have a BGP question!
I have not worked much with BGP, so i'm trying to find the best solution to configure the following:

We have 2 switches connected to an external AS# (eBGP). When using multipath connectivity to an external AS we are looking for the best way to use path selection. currently we use prepending AS to prefer a route to one of the 2 switches. But my feeling does not agree with me somehow. I cannot explain wy it is just a feeling, At first I thought "Weight" is the way to select the preferred the path.
But then is readed someware the following: "The Weight attribute is local to the router and is not advertised to neighboring routers" currently we advertise 2 subnets (In the future this will be more).
In the document is also found that MEDs (Multi-Exit Discriminators) can be used to assign a preference to a preferred path. but this is also true with as prepending.

So why should I chose Prepending over MEDs. MEDs can be overwritten with route-policy`s by the neighboring network administrators. where-ass prepending can not be adjusted.

What do you think is the best cause of action?
If you need more information please let me know. I'll try to explain as clearly as possible.

Thanks for you help
Palermo