I'd probably try to go for a nice grade 5.5 or 6 Mantle ('52)...might be personal bias because I happen to love that card, but I'd say you can't really go wrong with it...truly iconic card that even non-collectors will recognize, and I think if you had to sell it/liquidate in a hurry, you'd find more buyers than for the Plank (which I think is more of a niche' card for T206/tobacco collectors only...although there are lots of them out there too (including myself
))