gps receptor features

I'm searching a gps receptor for use with my pc and apple laptops, and
sometimes i will need use it in the car.

I don't know what features are necesaries for my use.

-would be prefer a SiRF chipset or only is necesary NMEA 0183 compatible?
-NMEA 0183 v2.2 o v3?
-is necesary more than 9600 bps? gps receptor send a lot of kB to computer?
-Number of satelites, diferences 8 vs 12? ¿in the practice is possible
receipt signal from 8 o more GPS satelites?
-fixation range of position, velocity <500m/sg, is this the max velocity
supported?


Sorry for my english :(

Para usarlo en un vehículo en movimiento que debería mirar?
La verdad es que no se si comprar el más barato que vea, o si por el
contrario es recomendable unas mínimas características técnicas.