When gigging regularly I generally used a 3-1/2"x1" bar. I still use that, but often use a 3-1/4"x7/8" (e.g. Dunlop 920), especially for pedal C6th and for 8-string plank.
Somewhere I have a 3-1/2"x1" glass "sitar" bar that's big but light - fun for a while but the lack of weight can lead to overshooting the fret

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My "dobro" bars are 3"x7/8". There are two, one is hollow (I think Jim Kerr made the solid one). My resonators are a 7st. and an 8st. Don't like stevens bars

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I also have a long bar, 3-5/8"x 7/8", but never really found a use - suppose that's what you mean by a "12 string" bar.
The 1" steel bar is good for hand excercises because of the extra weight but I could easily live with the "920" size for everything. BTW - I have small hands.
Incidentally, I bought a Dunlop 920 last month from an eBay shop in USA and the total (inc. shipping) came to £14.52 because that price is under the minimum import duty/VAT threashold. OK, so it took a couple of weeks to arrive, but it means I can afford a bar in every guitar case!

Just like Allan I keep them polished and in pouches/boxes and some are over 30 years old.