I think we need a proper, proper hard nosed defender of the Italian/South American/John Terry mould, who just wants to defend at all costs. Tarkowski is better than what we have at the present, so I'd take him and considering it's a free, or possibly a signing on fee, then it fits in with our finances at the moment.
Godfrey needs to beef up on his upper body strength as he gets pushed off the ball to easily. Holgate is a good enough squad back up player. Mina does have that defend at all costs but is too injury prone. Keane would need to continually work on his defending but may be past his usefulness. I think he should be sold if we get Tarkowski and another central defender.