I did a quick test last night using three different containers:
1. Aluminum Heineken 24oz "keg" can
2. Steel Progresso soup can (550ml capacity)
3. Aluminum disposible mini bread loaf pan (300ml capacity)
The Heineken and soup cans are almost identical in diameter. A Heineken can weighs about 30g (mine weighs twice this because I slathered silicone on the outside). The soup can weighs 65g. It is a two-piece can (no seams except at the lid) which I believe means that it is probably tin-free.
The loaf pan weighs 8g and is a rectangle. I was surprised this thin aluminum didn't burn easily. But it remained unscathed even when exposed to full flame for several minutes without any water in it. I wonder how it would hold up on a multi-day trip? (It's not a new idea:
http://web.archive.org/web/20061022080329/http://www.planetfear.com/product_detail.asp?d_id=9&c_id=19&s_id=512&p_id=11202)

I used 500g of water at about 18°C and ran the (canister) stove until boiling began. I used a simple windscreen, a foil lid, and I had the flame tuned kind of low, just as I normally would with a narrow can/pot. The start of boiling is somewhat subjective, admittedly, but I tried to be fair.
Results (time to boil / fuel used for 500ml of water):
1. 5:39 / 7.87g - Aluminum Heineken can
2. 5:28 / 7.77g - Steel soup can
3. 5:18 / 7.56g - Mini bread loaf pan (twice the values of one 250ml boil)
I don't see any significant difference here.