2015 or 2017 21.5” 4K iMac

[QCassidy352]

I still think the thing that makes the most sense would be to get a 256 or 512 GB SDD internal and then add cheaper external HDD storage as needed but that’s just my opinion.

I agree with that. If you can fit everything you have on a 512, I'd just do that. If you need an external either way (say you have 1TB of total data), I'd go with a 256 SSD and a big external drive. Just my $.02.

 

[jlseattle]

Get the internal SSD. That's the number one hardware upgrade you can do on the iMac. It's like:

Internal Fusion:
400-600 read/write speeds

Internal SSD:
1200-2400 read/write speeds

External SSD:
600-900 read/write speeds

Internal SSD is the best purchase you can make on your mac.

 

[jerwin]

The 21.5” got left at Broadwell (5th gen). So you will be getting a much more modern processor for your money by going with the 2017 since you will get a Kaby Lake (7th gen) processor. Might not be a huge difference given the storage options you are considering but every bit helps.

If h.265 4k "content" ever takes off in a big way, you'll want a Kabylake processor, which has the necessary DRM support that Netflix et al insist upon. you might have to install Windows, and hope that the Bootcamp drivers are "compliant" though.

 

[robeddie]

Sheesh they’re that bad? SSD is just so damn expensive

If you're up to it, you can add an aftermarket SSD yourself. It takes standard SATA 2.5 inch SSD's, so 1Tb drive is about $300, a 500gb drive around $160.

I just did the install of a Crucial 2tb SSD into my 2017 21.5 inch iMac last weekend. Running great.

Obviously you have to have the skill and the will to do the surgery yourself, but it's really not that hard if you're careful.
Both iFixit and OWC have guides on replacing the fusion drive.

Getting back to your original question, the 4k 2017 21.5inch iMac is a huge jump up from the 2015 4k iMac, due to it's massively better video card ... so that would be my recommendation.