best 1tb internal HD and most reliable external HD

i have used both of them and did not feel any difference , a slightly higher file transfer speed on wd
none have created any trouble for me
get what you like

WD Black is really good. For external drive ether: http://www.newegg.com/Product/Product.aspx?Item=N82E16822178745 or
or http://www.newegg.com/Product/Product.aspx?Item=N82E16822236576

Insofar as your query re which HDD to purchase I don't have any particular preference one way or another. No doubt you'll get responses promoting this or that disk. I just can't generate any excitement over HDDs these days. They ALL have the "slows" as far as I'm concerned and I doubt whether one consumer model is any more reliable than another. In my experience it's a crapshoot - nothing more. Now SSDs - that's a different story performance-wise.

Anyway, the real reason for my response is that I DO have a suggestion re purchasing a USB external HDD. (That's what you're referring to, right? - a USB device?)

My advice is NOT to purchase a "one-piece" commercial USBEHD. Rather, I believe you would be much better served by purchasing a USB enclosure or docking "station" of your choice and similarly a HDD (or SSD) of your choice.

The advantages of doing so are significant. First of all, virtually any USBEHD enclosure you purchase will accommodate both 2 1/2" & 3 1/2" drives. That's a real advantage. Then you can purchase the HDD YOU want, not the HDD that's installed in the commercial product. Rest assured the drive you purchase will invariably prove superior to the commercial product. And you can select whatever disk capacity YOU want. Another advantage is that the HDD you install in the USBEHD can always be easily removed and installed in a PC should that need arise.

Still another significant advantage is the fact that by using a separate USBEHD enclosure + HDD you will have UNLIMITED capability to utilize any number of different HDDs/SSDs for whatever purpose(s) you deem necessary or desirable.

All in all there are really no downsides to purchasing a USBEHD + HDD in comparison to purchasing a commercial one-piece product. And you will have an enormous choice as to the USB enclosure that appeals to you. One type is the so-called "docking station", see for example http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=blacx&N=-1&isNodeId=1

There are plenty of other types of enclosures. Right now, as an example, we're using the Orico 6518US3 model. See...
http://www.amazon.com/ORICO-6518US3-Super-Docking-Station/dp/B00CBPB4PM
Newegg also carries this model. And there are many others to choose from.

And it's child's play to install and/or reinstall a HDD in & out of a USB external enclosure - whatever the type.

Anyway, give it some consideration.

Both are worth it. I would get the WD. As urbanrider said.

These days HDD are commodity items, and there are really 3(?) manufacturers in the whole world, they just re-brand them.

So which one is best, depends how you use it. Do you want quiet or performance?

Reliability... did I say commodity? The best reliability is your back up plan, and at the current price, I don't see why one wouldn't do it.