Kind of tricky question. DoW1 has an enjoyable single player campaign, but it's very simple. It's in the "AI occasionally gets units and sends them at you but doesn't actually think for itself" camp. The game has pretty decent AI for skirmish mode, but the campaign doesn't use it. Except in the case of Dark Crusade's campaign, which is a world map that plays more along the lines of skirmishes.
DoW2 has a slightly better campaign, however it's less of an RTS. No base building whatsoever in the campaign mode, and you only control a maximum of 4 squads, who can level up and pick up loot and fight boss battles. It's more like a Warhammer 40,000 Diablo. DoW2 also doesn't have as enjoyable skirmish AI to play against, and a hell of a lot fewer maps, races, and units.
As much as I prefer DoW1, it mostly depends on if the RPG-lite campaign of DoW2 sounds better to you or not, or if you'll play singleplayer skirmishes against the AI. Also depends how much stock you put in graphics, because DoW2 is much prettier. DoW1 certainly isn't bad, but it doesn't have much eyecandy nowadays. Also worth noting that DoW1 is a much larger game, especially with expansions. The number of units a single player can field is much higher than DoW2, and squads can reinforce anywhere on the map. It tends to have much, much larger battles than DoW2, and supports 4v4 multiplayer/skirmish whereas DoW2 goes to 3v3. Overall I'd recommend DoW1 over DoW2.
If you do go for DoW1, I'd recommend the platinum pack and ignore Soulstorm. Soulstorm would be nice to have for the sake of having all of them, but it's by far the weakest of the DoW1 expansions and has quite a few bugs.