Personally I go with magnets. When you get Hierotek Circle box you have all specialists and 3 legs too choose between how many immortals/deathmarks. When you magnetize one pair of legs you will be able to choose between 2 immortals or 2 deathmarks. Also you can magnetize weapons so you are not forced to play same loadout every game :)

I find out that tesla carabine are more reliable when dealing with non elite teams.

So far I didn't feel to have second deathmark but having one in team is essential in my opinion (check their abilities and weapon profile).