Walker had a 1.044 OPS while playing for the Rockies home + away, he deserves to go in the HOF well before Helton. Walker was .965 OPS overall while playing about 40% of his games for two other teams (much lesser hitting parks in St. Louis and Montreal).
Helton is a very good 1B with the glove, Walker was a better RF - and that's a tougher position.
Walker was a great base runner, Helton is not.
Walker was a borderline great playoff player, Helton is not.
Walker > Helton