What do you want to do with your external drive? That will determine what the requirements are for both the drive and the enclosure.
IMHO at the current state of the art,
For BACKUPS HDDs have more than adequate speed, are significantly less expensive per TB of capacity, and are better suited for long term storage. USB 3 would be fast enough and has the advantage of being backward compatible to USB.
For ALTERNATE BOOT DRIVES an enclosure with a USB 3 interface the USB will be the limiting speed factor not the drive and a 7200 RPM HDD will work and a LOT cheaper than SSD. An enclosure with USB C / Thunderbolt 3 can take advantage of the significantly greater speed of an SSD. At that level the limiting factor becomes the SATA drive interface in the enclosure.
For AUDIO/VIDEO PRODUCTION where price is no object and high speed is the name of the game, USB C / Thunderbolt 3 interface with a really high speed PCie based drive or perhaps a RAID enclosure would be the choice.
Your future computer will most likely be USB C / Thunderbolt 3 and compatible with USB 3, Thunderbolt 2, etc with appropriate adaptor cables. SSDs come as a complete package not a chip set and which is best is more often based on "what I bought" rather than actual statistics — besides that if you don't like what is available today just try again next week and there will be other options available. (Personally I have had good results with OWC's offerings but have no experience with other brands.) I have no idea what a hybrid enclosure would be as all of the bare enclosures I am familiar with are standard SATA. The highest end external SSDs like the high end internal SSDs are soldered in place.
There are lots of opinions pro and con about cooling fins, or fans, or nothing but in the only extensive test of drive reliability (conducted by Google Labs) they found heat was not a significant factor in drive failure. That was conducted on HDDs and I don't know of similar study on SSDs. My personal preference is an enclosure with at least a semblance of a heat sink (
ie. metal contacting the drive to help with heat dissipation. An on/off switch can
occasionally be useful but as far as I am concerned while it can be nice to have, it is in no way essential.
As I sit here I see five external enclosures,
- a Thunderbolt 2 RAID 5 enclosure with four 1TB 2 ½" HDDs used for Time Machine backups,
- a USB 3 enclosure with a 4TB HDD and a Superdrive that is used as a second Time Machine backup ,
- a USB 3 bus powered enclosure containing an SSD recovered from a defunct Mac mini that I use for experimental purposes,
- a 120GB OWC Envoy Pro Mini setup as a TechTool ProToGo emergency boot and repair drive that is very convenient because of its compact form factor,
- a bus powered USB 3 enclosure with a 1TB HDD that I clone the last working configuration to before installing the next beta release. I tried to talk myself into getting an SSD instead of HDD for that last drive, but even I could not justify the 5X increase in price and the one I really wanted cost twice that amount!