Some confusion here… nrf2401 and variations is just the chip by Nordic. You’ll have to go for some module implementation, and Sparkfun created some confusion by using the chip names on their modules. You can find modules from various manufacturers, not only Sparkfun.
I’m using the TRW-24G module by Laipac built around the nrf2401a chip, I used the Sparkfun nrf2401a using the same chip (not recommended), and the Sparkfun nRF2401L+ module. They have some minor differences, and when I recommended using the nrf2401 I referred to the family… anything within it would be better suited for your data transmission problem than the 434 and 315mHz modules.
If you’re concerned about range, I’d recommend using the Laipac, not the Sparkfun modules. Don’t ask me why, but even the module with te same chip don’t have the same range. Maybe the shielding or the different antenna makes a difference. The only advantage for the Sparkfun module with the nRF24L01+ is the built-in ACK and retransmit features, but it’s not such a big deal. The higher max data rate is not so useful if you’re concerned about range and will have to keep it low to 250kbps anyway.
Despite what the manufacturer says, which sounds like sales argument from marketing people, I wasn’t able to get the 434 and 315mHz modules working with UART at more than 500bps, and even that wasn’t very reliable. They can’t keep transmitting for a long time, so it will drop signal a few seconds after the first pulse. Not only that, but those frequencies are very crowded too, and you’ll get a lot of corrupted data. If you’re building a robot that will run outdoors like mine did, every time someone around turn the car alarm on or off, expect to get interferences. The 2.4gHz frequency is very crowded, but the nrf2401 modules have the shockburst mode to transmit the whole buffer in a single short burst, so the chances of getting interference are much lower.
The 434/315mHz modules are perfect for making small remote controls, like those used by cars and home security systems. I get them working easily by coupling with a pair of HT12E/HT12D encoders, decoders and currently have one working like that for my home automation system. If you can control your vehicle motor and servos with 4 bits per frame, then you can use it, but I think it’s worth mentioning I was doing the exact same thing with them (controlling a robot motors and servos) when I got tired of struggling with it and decided to try with the nrf2401 family modules.
About the range advantage you presume those modules have, don’t go for it. With the TRW-24G module with the nRF2401A chip, I got a greater range than these modules, and than the Sparkfun modules too, including the one with the same chip. With the much higher data rate is easier to also implement a better protocol to deal with lost packets and force the range to the limits. Maybe the only real advantage is that 434 and 315mHz signals need a much bigger obstacle to be blocked, but it’s not such a big deal.