Best spot-start options?

[Fantasy GM]

I play in a H2H points league that has a limit on pitching starts we can use in a week. I have 3 open starts, but four fringe SP:

Lance Lynn vs Astros (tonight)...he's facing a very watered-down lineup, possibly his last pitching start of 2012 (USED THE START )
Chris Carpenter @ Cubs (Friday)...best SP of the four, though it's his first start this season
Ivan Nova vs A's (Saturday)...will likely see run support and can go 6 IP, but walks can hack into his pitch count
Alex Cobb vs Blue Jays (Sunday)...very good at home, but has alternated solid starts with trickier ones

Which three starters should I use? Quality starts are valuable in our league (in addition to the usual point-scoring categories).

[Element]

I'd scratch the start with Cobb. It came down to him and Lynn, but Lance looked strong against the Dodgers his last time out and Houston is a juicy matchup.

[Fantasy GM]

Houston is a very juicy matchup. I'm trying to determine which 3 SP give me the best opportunity for a quality start (and more). Do any of the other three matchups stick out or are all the SP even?

[Fantasy GM]

Apologies for the "bump." Edited the original post and also noticed how the A's burned through Verlander tonight due to taking pitches and prolonging counts. Would Nova vs Oakland be the riskier matchup? The other option is Cobb vs Toronto.

[Element]

Nova looked excellent in his last start. I would start him vs anyone right now. His stuff plays when he's right.