Stuck between two (Normal)Chrom Builds!

Note: If you wanna go straight to the question, there's a TL;DR at the end. Thank you~!

My first ever Chrom that I had summoned was a +Def/-Res Chrom. I consider him an amazing unit, and I promised that I'd keep this Chrom and make him my first ever "+10 unit". Currently, I'm at "+3", and I noticed I can start changing his build.

My current Set-Up is:
Weapon: (Bond) Falchion
Support: Reposition
Special: Aether
A: Earth Boost 3
B: Vantage 3 (I don't plan on changing this - it has helped me a ton)
C: Spur Def 3 (I'll get to this in a moment.)
S: Quickened Pulse

However, his stats has increased dramatically ever since he had been "Summoner Supported", had his weapon refined, and has been merged up to 3. As it stands now, his stats are as follows:
57/56/25/37/20

I've been thinking of finally slapping DB3 (since I finally got fodder for it) on him, but I'm not sure. With his current build, on the enemy phase he can reach INSANE defence levels thanks to my bonuses, his refinement, his merging, PA!Azura/PA!Shigure, and his unit support.
However, the same can be said for his attack IF i decided it would be best to focus on that... just on the player phase.

I really wanna make him one of my top sword units, as I don't care about LH!Ike we'll be getting soon or my Soleil... AT ALL. With the way he is now - he's a fantastic unit in my opinion. I just need to know if I'm in the right mindset.

TL;DR, the question is: Would I be best off making Chrom a player-phase unit with DB3, keep him as a enemy-phase unit with EB3? (I think I'll swap between the two when needed, but this would be for his main set-up.)
Bonus: If possible, can anyone give me tips on what a good C-Slot can be?? I just can't decide with him right now.