On the relative ease of E2 dehydration
The rate of reaction depends on how stable the transition state is. In both E1 and E2 good leaving group is present along with presence of a weak and strong base ,respectively. This leads to an alkene type of transition state in E2 mechanism and a cationic type transition state in E1 mechanism . Both these transition states gets stabilized by the electron donating ability of the attached alkyl groups (i.e By Hyperconjugation and Inductive Effect).This leads to the increase in rate of reaction and thus the secondary and tertiary alcohols are easier to dehydrate than the primary alcohols.
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