Who should I choose for my 5th rookie defender?

[MontyJnr]

Have already locked in Terlich, Goodes and Stevenson after showing good form across the NAB cup. The mature aged Pittard has my 4th spot at the moment, after cracking 100 against Sydney at the weekend and I can see his JS being better than some of the other rookie options. Is it really worth spending the extra coin on a Brown or Vlastuin over guys like Colquhoun, Heath and Docherty though?

Brown, although scoring 95 in a practice match against Freo, scored a dismal 18 against Carlton despite playing 93% of the game! Would you fork out $135,500 for him?
Vlastuin has been OK, but he didn't crack 50 in either of his full-length NAB games and could be a sub candidate. Is he worth the $159,500 price tag?
Colquhoun scored 100 against Melbourne, only 29 the next week against West Coast playing only 59% of the match and rounded it off with a 62 against Sydney. Will this kid get regular games?
Docherty's average doesn't look great as he only scored 5 in the NAB cup grand final, but he only played 14% of the game. Does he have a spot in Brisbane's 22?
Heath scored 71, 45 and 63 in his 3 full length NAB games, I don't know much about him though. Will he get games?

Would very much appreciate any further insight.

[felsty]

I'm in the same boat ie. same 4 players picked and don't want to spend coin on vlastuin and brown. I would say a toss of a coin between Heath and Docherty. Remember Doherty is a number 12 pick so can play some good footy. Both have good js and good scoring potential. Either will do if named round 1