The answer probably depends on the exact class of receptor you are studying.
EGFR and other receptor tyrosine kinases (RTKs) show activation by dimerization rather than activation by conformational change; that is, ligand binding induces dimerization of the receptor, and dimerization leads to downstream intracellular signaling cascades. However, dimerization brings the intracellular domains together which allows them to interact, causing a conformational change that activates the activity of the intracellular kinase domain, so conformational change is still involved. For a detailed look at the activation mechanism of RTKs see this review from the Kuriyan group:
http://www.annualreviews.org/doi/abs/10.1146/annurev-biochem-060614-034402WRT agonists, antagonists and conformational change, probably some of the most relevant work has been done on GPCRs. I'd probably look up some of the recent structural work by Kobilka and Lefkowitz (e.g.
https://www.nature.com/nature/journal/v535/n7612/full/nature18636.html). I am not too familiar with this field, but I'm not sure how well tested the allosteric models are for GPCRs given the small number of structures available for these receptors.