I'd recommend collecting whatever is currently in stores now, e.g. Transformers Prime. If you wanna build a "G1" collection, I'd recommend going for "Classicsverse"*; cheaper, easier and quite frankly, the toys are generally better made too (joys of modern toy engineering). See this thread for lots of side by side comparison photos between G1 and Classicsverse.

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*an umbrella term for Classics, Henkei, Universe, Generations, United & Reveal The Shield