Can anybody suggest me the highest speed DSPs available in the market now. Also, what would be the best for a filer design application a DSP or an FPGA?
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
This question is too broad and without some more information about the application and the constraints impossible to answer. For actual filter "design" a dedicated DSP is probably not a great choice and you are better off with a high end general purpose processor such as an Intel Xeon or then new-core I7s, Xeons also work well in multiprocessor setups.
Filter implementation really depends on whether you have high-complexity/low-clock or low-complexity/high-clock rate. Best solution for an 100k+ tap room response filter for audio, or a line EQ for a cable modem are totally different. In general for low complexity applications ASICs are faster than FPGAs are faster than general purpose DSP processors.