Love controllers (Or ones like them) are cheaper, but you have to do all the wiring yourself. On the up side, they lend themselves much better to a flashy installation.
Johnson and RANCO are easier because you just have to plug them in. But you pay for it, and they are ugly (IMO)
They both do the exact same thing - Flip a relay when a temperature probe says it's too warm/cold
Speaking strictly of digital controls, accuracy is irrelevant. The probes may be poorly calibrated to some degree (heh), but the controller will always turn it on if it's told to, at the same temperature, every time. You might program it to turn on at 65, and it will turn on every time the probe says it's 65 in the chamber. But the probe may be off by a degree or two - so you would just have to calculate some offset when you program the controller.