Walrein's not the best, but I wouldn't call it bad. Vaporeon's my tried and true for that role, but since you're looking for Pokemon you haven't used and aren't keen on Walrein there's Lapras, Wailord, and Starmie. Though Ice Beam/Blizzard aren't available as a TM yet unless you're modding the game, you've still got options for Ice moves with all of them. Though, I do think Walrein's your best bet to fit the role - especially if you're looking for stuff you haven't used before.