RS-485 if you do not want to get into some of the newfangled stuff such as LVDT (I wouldn't).
What do you gain by RS-485
1) Differential signalling = virtually immune to noise. I had a case of an industrial 485 that had run error free for years when it was discovered that the cable shield was not connected.
2) A decent transmission speed
3) B&B electronics make a cheap interface to your PC nothing "strange" there.
4) Industry standard

As for current loop, that was good for the teletype at 110 baud.

Erik