The Model 21 would be easier to move. You buy an Ithaca either accept the haircut you're probably going to get or keep and use it.
Winchester boys like Colt and Parker Bros. brethren have "deeper pockets". If you can swing the $5000 to $6000 for original gun in great shape the 3" Model 21 is not a bad shotgun. Big plus you get the same weight and handling as 2&3/4" gun but with 3" chambers so you can use nice larger size shot in 3" cases Kent Tungsten Matrix, Fiocchi 'Tundra' or Kent Bismuth shells for wildfowling. The Winchester seems to hold value though the prices for field grade stuff have not been going up in recent years.
For most part Ithaca boys have holes in their pockets. The wonderful field grade 37 pump in very good shape can be had for about $300 or $50 to $75 more than 30 years ago. Flagship transitional 'Supreme' from mid-50s with solid rib, nice wood and Ithaca Sunburst pad with aluminum backing in top shape (dry closet gun) went for only $500 at LGS. Equivalent gun from Winchester model 12 line would bring well over $1000.
