Look at your own team needs, I know what I would get, but then again, I don't have a clue how your team does a lot of machining or whether the need really goes toward the lathe or the mill. So rather I will outline the pros of each and let you decide which might be the better choice.
Lathe:
Pros:
- If you have the patience, any cylindrical part (and some square) can be worked with to great precision.
- Speeds up the process of working with cylindrical parts enormously. There have been times when all six of our lathes have been used at once. (Curse CAD and their complicated parts... Oh, wait, I am CAD... I guess I'll have to remedy that...)
- Lathes also allow for custom taps on parts. Example: Oops, a screw for the gearbox got lost and the replacements won't get around for a few days. An hour later, "Look! a new screw! Now we can finish the robot!"
Cons:
- Bits, without them, all the pros vanish, especially if you can't sharpen them if they're dull. HAVE AN APPROPRIATE GRINDER TO SHARPEN AND SHAPE THE BITS TO AVOID THIS.
Mill:
Pros:
- Drilling all those holes with a drill dress just got a LOT easier. No longer do you need to worry about placing a center punch exactly where you need to because you don't even need them.
- If you need aslots in a shaft for a key, you also need a mill. Nothing else will do a quality job.
- If CNC capable, round cuts can be made, however, This depends on the machines capabilties.
Cons:
- Many of the things mills excel at can be divvied up between other machines to achieve the same result although using the mill would still be best.
Wow, what a long post. Anyways, I only listed a few of the reasons you should pick one or the other. So read other's posts and decide for yourself.