Traps/? for high levels?

Building a new defender to pair with a friends WP/something tank, with the aim of having the nucleus of a team for high level TFs eventually (we usually take a year or so on projects like this). I'm set on the Traps primary, and am wondering what to pair with it for a secondary for high level content. I would do Sonic, for AV fighting (which is the only thing much more than speedbumps for large high level teams), but already have a cold/sonic and two kin/sonics on various servers, so I'd like something else. I'm also ruling out /rad since I have a couple of rad/rads, and you don't really need the defense debuff with Acid Mortar. I was considering /Dark, but having played a couple of them to mid levels I'm dubious about having to run back and forth from melee to drop traps to range for Nightfall, the narrow cone.

I'm figuring either Dual Pistols (for varied debuffs/damage type), Cold (for the AoEs) or Archery (for Rain of Arrows) would be the best to pair with, but haven't played any of them at high levels, so would like peoples opinions on which might be best. Cost is not an object for a final build.

I find Traps/Dark works out very well, myself. You do have to run back and forth a little, but it's all worth it when Tenebrous Tentacles keep things grouped up for your mortar and the -ToHit from spamming TT and Night Fall effectively softcap you when your Force Field Generator is factored in. Which lets you toebomb pretty reliably.

However, /Cold or /Archery would both be good picks, too. You can't go wrong pairing anything with Traps/, really. My only concern with /Cold would be that Acid Mortar can scatter things a little, so you might have a bit of trouble keeping things in Ice Storm and Blizzard... but I suspect PGT + the slows from those two would do pretty well at keeping them put.

I'll second the traps/dark vote. I'm currently leveling one up and he's 29 atm. I haven't even started IO'ing him out, actually he's sitting with a few yellow enhancements and open slots from combining SO's, and he's still a beast.

In regards to the running back and forth, I think it's absolutely worth it. Between Acid Mortar and Caltrops, you get alot of scattering. Tenebrous Tentacles are a wonderful way to counteract this.

Pretty much anything works well. AR is quite nice for a TF build. You get good AoE to help clearing out the regular groups and Ignite uses the Blaster damage scale so you get more damage against AVs. Plus Traps plays well when you're in near-melee range and so does AR.

My Traps/Dark is a tank.
My Traps/DP is a scrapper.

Depending on the secondary and how you build you'll vary within that range of performance. You could make almost any combination work. With the dark I tend to try to stay toward an edge of melee to get the most of my cones while still laying traps next to the enemy. With the DP I just wade in and let loose. The dark is more survivable both Pre-IO and Post-IO, although Post-IO the defensive performance gap is smaller.