I go BLM for T10. Not enough movement to justify the switch and in general a BLM vs SMN of equal level and gear with minimal movement on a target will end in BLMs favor. That said the add phase is an exception, however I've found that the length of the add phase and the fact I can flare a pair of adds outweighs the higher damage on the SMN during that phase. We still run with a summoner for that fight though as we find it slightly in favor of range vs melee (just easier to spread, easier to dodge blue circles of doom, less stacks are lost due to charges or tethers).

For T11, SMN LOOKS to be the best bet, I'm still doing some math and switching between the two on each lockout. But preliminary tests are showing SMNs ability to multi-dot during the add phase + the ability to not be rekt by nerve gas could outweigh the BLM higher single target potential.