I would say Vaporeon probably works better as a special wall, due to its better supporting moveset (Wish passing, threat of Heal Bell to clear status, etc). Suicune's moveset is better supported to supporting in Doubles with Tailwind, Ice Beam, and water-type STAB, but its best use in singles is the wonderful, glorious CroCune set (Scald/CM/Rest/SleepTalk).
Depending on your team's needs, I would recommend Vaporeon over Suicune, but you could try both using sims like Showdown before you make your decision.