My thought has always been to long first - you can always take some off later. You never mentioned twist and with 100-gr as the lightest bullets, at a minimum I'd go with 9-tw or even a little quicker twist.
Start long, one can always shorten is my recommendation too. I rebarreled a Savage 110 to 250 Savage and the barrel I used came in at 26". I really like that length as it balances nicely for off hand shooting and the added velocity doesn't seem to hurt. The twist was advertised as 1:10" and it is pretty accurate with Hornady Interlock 100 gr SP and 117 gr RNSP, Sierra 90 gr Matchkings and 117 gr HPBT, and factory 100 gr Remington Core-Lokts. I'm sure it would be more impressive with someone else behind the trigger. I am satisfied with the 1:10" twist but if I were to order a barrel rather than pick up a clearance one, I might go faster to better handle heavy lead less bullets if I so chose.