What ELFORM do you use for different elements and Why? in the context of LS-Dyna

In terms of speed and robustness I would rank shell formulations as follows:
1. type 2
2. type 2 with BWC warping stiffness and full projection (see BWC and PROJ in *CONTROL_SHELL)
3. type 10
4. type 16 (Type 16 shells require approximately 2.5 times more CPU than type 2 shells.)
5. type 7
6. type 6 [1]

The last 3 formulations listed above are fully-integrated (4 in-plane integration points) and thus do not suffer from hourglass modes [2]. Generally speaking, the underintegrated elements tend to be a little too soft. By using stiffness-based hourglass control (HG type 4) and a reduced hourglass coefficient (say, .03 to .05), the behavior is stiffened slightly and so this hourglass combination is generally recommended for most applications of the underintegrated shells. For very high velocity/rate problems, viscosity-based hourglass control is recommended.

Accuracy:
From an accuracy standpoint, shell type 16 is preferred over the underintegrated formulations provided the following are true:
- initial element shape is reasonable
- element does not distort unreasonably during the simulation
- Used together with hourglass control type 8, the type 16 shell will give the correct solution for warped geometries.