Here are some guesses:
- When you choose not to consume either animal products or energy, there isn't a one-to-one correspondence with how much is consumed in total. Less consumption decreases prices, and decreased prices lead to more consumption. So to know how much less product is consumed, you need to know the elasticity of price with consumption, and the elasticity of consumption with respect to price. This article from Peter Hurford has some links that might be helpful for thinking through these for animal products. I haven't looked for analysis of the elasticities for e.g. energy usage, but I strongly suspect that decreased energy usage has almost no effect on total energy usage, especially if you account for higher fossil fuel prices leading to increased research in clean energy (and lower prices to delaying research).
- Please comment with more useful references for these questions (both energy and animals) if you have them.
- If the two changes are equally effective, then the one with an easier "line in the sand" may be better for motivation/self-control reasons.
- The one with the line in the sand ("I boycott animal product!") may be more effective as a symbol for a political movement. (I personally suspect that all of these changes have negligible direct effects compared to their potential effects as symbols in political movements.)
This is all very speculative, of course! Some of these thoughts were already touched on in the FB discussion, but I decided it would be useful to pull my thoughts together in one place.
Many EA's seem more attached to the direct impact of not eating animal products than I am, so I think (1) may be the most important.