You mentioned building a computer so I am going to assume you mean a desktop pc. There have been quite a few changes since your last build. Part of the changes are related to ssd price reductions. Part of the changes are due to the new SATA 3.2 standard that was finally adopted last year.
Currently the standard 2.5 inch, SATA 3, 6Gb/s ssd's are considered to be the "sweet spot" for consumers and casual gamers. We've had some sale prices approaching $0.50/GB. Typically a consumer or casual gamer will have a 256GB ssd for the operating system, software applications, utilities, and favorite games and a hard disk for data storage, additional games, and backups. If you have a perfectly good hard disk drive, then you can use it for your new build.
Last year the new SATA 3.2 standard was officially adopted. It includes provisions for several different types of ssd's - Standard SATA 3, mSATA, PCIe, and M.2 NGFF (next generation form factor which is also PCIe). The new standard marks the beginning of the transition from SATA based drives to PCIe based drives in an effort to overcome the SATA data transmission bottleneck. It is all in the early stages of development. Right now we have a bit of a problem with motherboard manufacturers. The motherboard manufacturers have some flexibility with onboard headers / connectors for ssd's. The manufacturers opted to add the new M.2 NGFF header / connector instead of a dedicated PCIe 3.0 x16 slot for PCIe based ssd's simply because it was less expensive and helped keep costs down. At first it seemed to be okay because M.2 NGFF was for PCIe based ssd's. Then the manufacturers did something odd. They severely limited the number of channels / lanes that could be used to just 2 instead of 16. In addition one of the PCIe 3.0 x16 slots was disabled if an M.2 NGFF ssd was used. It gets worse. Last year Samsung began mass producing their XP941 M.2 NGFF ssd. Samsung has very lucrative contracts to supply "off the shelf" pc companies like Dell, Lenovo, and Apple with OEM versions of the XP941. The XP941 uses 4 channels / lanes to receive and transmit data. As of last month there was only one desktop motherboard available that could properly support the XP941. All others require the use of an adapter card inserted into a PCIe slot on the motherboard. Based on what we know is coming from the ssd manufacturers it is safe to say motherboard manufacturers have a lot of catching up to do. This is definitely a "wait and see" what happens situation.
For desktop pc's I normally recommend Samsung ssd's. They perform exceptionally well and have a proven track record. The 840 Pro you mentioned was Samsung's flagship model. It was recently replaced by their new 850 Pro model. The Samsung 840 EVO which costs less is the number one best selling ssd in the world. Samsung announced they would be releasing an 850 EVO model to replace the 840 EVO in the very near future. Among the other brands, Crucial, SanDisk, and Intel are worth considering. The SanDisk Extreme Pro you mentioned is another excellent choice.
I maintain the ssd database listed in a sticky at the very top of this forum section. Here is the link:
http://www.johnnylucky.org/data-storage/ssd-database.ht...
Scroll down to the brands and models you are interested in and follow the links to the technical reviews.
Finally, the hybrid drive combinations never really caught on so there aren't very many to choose from. There's no point to in using one when the OS, software applications, utilities, and favorite games can be installed directly to an ssd. If a laptop can only accommodate one drive what we are actually seeing is consumers using an internal ssd and an external hard disk drive.