Raticate has a Base Stat Total of 413
Furret has a Base Stat Total of 415
The difference is not big.I would go with Furret
1. It has a good movepool,good stats and It learns 5 HMs
2. It can learn Normal,Dark and Psychic moves during leveling up.
3. Its Defenses may be low but it has a good Speed and nice Attack Stat.
4. It can learn a Big Variety of tutor moves, such as Aqua Tail, Fire Punch,Ice Punch, Thunder Punch.It can learn a lot of TM moves, such as Brick Break, Facade,Shadow Claw and even Giga Impact.
5. It is better than Raticate beacuse : it is quick and likes to chase RATTATA. (SS pokedex entry :P)
So yeah. Furret it is