Value is best defined by the price per gigabyte in a storage device. This used to be held by smaller capacity drives but now higher ones are starting to offer a overall value. With a price of $160 and a capacity of 240GB, the Crucial M500 ends up with just $.67 per gigabyte to offer a solid value. In addition to offering a nice capacity for the price, the drive also offers some solid performance thanks to its custom Marvell controller with roughly 500MB/s read speeds and 250MB/s write speeds. A very close alternative is the SanDisk Ultra Plus 256GB drive that offers a $.68/gigabyte pricing but has slightly higher storage capacity and slightly better write speeds.
Performance in solid state drives is reliant upon the memory chips, the drive controller and what interface version it uses. The highest performance drives now require that the systems have a SATA III or 6.0 Gbps interface on the computer and drive. If you want the best performance possible without getting too expensive from the capacity, than the Samsung 840 Pro 256GB drive offers a good balance between performance and price. Burst read speeds reach up to 540MB/s while write speeds are a bit slower at 520MB/s. It is important to note that this is a Pro version rather than the standard 840 series which has less write performance and a shorter warranty. Priced around $215. An alternative option is Samsung's new 840 EVO 250GB drive that uses a new style of NAND with a Turbo Write that offers it very strong performance but with a three year warranty against the Pro's five years for a lower price.
If you want the most capacity possible out of a drive and aren't too concerned about costs, then the Samsung 840 EVO 1TB drive is an obvious choice. This drive uses a new type of triple cell NAND to offer higher density memory chips. Performance is still quite good thanks to the use of the new Turbo Write capabilities from the Samsung memory controller. Speed can reach up to 540MB/s for reads and 520MB/s for write operations. Pricing for the drive is up there though at roughly $600. If you don't mind giving up a bit of performance and storage space, the Crucial M500 960GB drive is a bit more affordable at $550.
A number of PCs that use Intel processors and chipsets can accelerate a hard drive with a solid state drive through a caching system called Smart Response Technology. Essentially, a small SSD drive up to 64GB in size can be used as cache for frequently used data to improve performance. In this size range, the SanDisk Ultra Plus 64GB drive offers a good level of performance especially with data reads that are critical for the caching system as writes are typically still restricted to the speeds of the hard drive it is caching. The only downside is pricing is still around $75 which isn't great at a per GB rate. In fact, a good alternative is to buy something like the Sandisk Ultra Plus 128GB drive for just $30 more and have both a 64GB cache plus an extra 64GB of fast storage space.