Long term storage: use 2tb, 3tb or 4tb internal drives?

I'm moving towards a system of having data backed up on internal drives I'll use with a OWC Thunderbay and separate external drives as well.

I'm trying to decide what size internal drives to use. I'm choosing between drives that are 2tb, 3tb and 4tb's large. I imagine I get more bang for my buck with 4tb. I'm tempted to go that route. I'll have everything backed up so I don't worry about the fact that, if it fails, it's 4tbs.

That said......any other thoughts on this matter? Is there another way to think/approach it? Just brainstorming before buying stuff.

Thanks in advance!!

Which Mac are you referring to? Larger capacity drives may not physically be suited for a MacBook Pro for example.

I agree with Charlie. You need to do your homework, to see what is available for your machine, and then decide, what you want. IMHO, if you going to have a OWC Thunderbay, where you could possibly put up to 12GB, I wouldn't fret too much on the size of the internal, and would be happy to settle with a 1TB HD or a 512/750 SSD.
I love the speed I have with my SSD in my Optical Drive Bay in my 2012 13" MBP, and I also use the original External HD as my first call as a backup. I have a 240GB SSD and 750GB HD, and I SuperDuper backup the SSD to the 750 HD, and then Time Machine the 750 HD.

Ah. I wasn't clear. I have a MBP with a 500GB hard drive. But I'm thinking about the externals I'll put in my Thunderbay. I'm not sure which ones to get. That's what I was asking about.

it depends on how you are going to format them.

Fat32 supports 1TB and 2TB on mac however on windows it might not read the data and is limited to file sizes of 4 gig's only anything after that you have to format in ntsf which does not work well under mac or mac os x extended

Honestly if you have the money go with the 3 TB option you would be much happier and worry less because you have enough space on the drive as a leeway so if you decide to store larger files you don't have to worry about the hard drive space

I'm going to be using it for editing film....