I've got a metal one, I don't like it and I'm always looking for somethign that I like better. Ideally I want a scuttle, but they're usually too big or ugly.
A porcelain or ceramic bowl is the way to go. You could use a heavy coffee mug too. The ceramic type material holds heat better than stainless steel. As for size I have a bowl I got from Target that has a wide flat bottom. This size allows me to whip up my lather better than in a mug.
I found a hollow metal bowl made for sauce.
I took out a square piece of the outer wall to access the gap between the walls. Made a funnel out of a eggholder and some silicone.
Works extremely well, the metal gets warm instantly and preserves heat for a longer time then ceramics, imo.
I found an inexpensive easy-to-find (in the US), and effective bowl to use for mixing lather. It is a 12 ounce dessert bowl made by Corelle. It is 2" in depth and 5" in diameter.
Features/benefits
1. Inexpensive at $3
2. Easy-to-find at Walmart, KMart, Target
3. 2" depth allows you to not have to reach deep.
4. Bowl (rather than mug) shape...no corners that tend to clog with lather
5. Not too big...you can grip it in your hand
6. Not too small...you can move your brush around and get a fine lather
7. Made of a material that will absorb heat (perhaps not as good as pottery, though)...keeps lather warm
8. Material is resistant to breaking/chipping
This bowl tends to come in white. If you can find it in sandstone (color), I'd recommend this. Sandstone makes it easier to see the lather.