All pure? That's no fun in my opinion, I like my decks to be a blend of colors like my main one. They're a little harder to play but for me that's half the fun. Plus pure decks are somewhat more easily predictable as they have a more limited array of cards that they can use. Hybrids have the disadvantage of not always having enough mana for a specific card but it balances out in that they're slightly harder to counter.
One fun combo: Avacyn, Angel of Hope (White) paired with Elgaud Shieldmate (Blue) plus Avatar of Hope (White) paired with Elgaud Shieldmate (Blue) plus Melira, Sylvok Outcast (Green).
Avacyn: 8/8, Makes controllers permanents all Indestructible.
Avatar: 4/9, Can block any number of creatures.
Melira: Negates Infect and causes all -1/-1 and poison counters to disappear while she's on the field. (If I recall correctly)
Shieldmate: It AND the
creature it is paired with both become Hexproof.
Mentioned that combo to a friend and their eyes went wide with fear at that plus Primordial Hydra paired with Elgaud Shieldmate.