Welcome to Librarium Online!
I'm pretty much looking for an army that is fun to paint (i.e., not too easy, and not too tedious at the same time) and that doesn't suck under the new 8th edition rules (like Wood Elves apparently)
pfff you really have some difficult questions man...
Do you like to paint thousands of models a night?
Warchief Diggah o da Bloodmoon Squiggahs
Are Daemons still competitive? I don't know what's good any more, haven't really been following the 8th edition stuff.
Daemons could give you a lot of variety, at least. Skaven and Beastmen were the last two books out, if memory serves, but I haven't really looked in to the model ranges of either.
In short I don't really know why I'm attempting to answer your question when I KNOW NOTHING!
Honestly mate, best advice here is go with whichever army you like the models for. 8th Ed has shown how dramatically a rules-quake can shift army viability- Whoever expected Goblin hordes to be in ascendency? If you pick your army to match a rules-set (ie "competitive" armies) then eventually you'll be let down when the rule-set shifts. If however, you picked an army because you liked the models, the theme, the conversion oppotunities etc then you'll never tire of them and your enjoyment will be greater because of it.
No more NG spearmen, thanks! Now I need some pump-wagons!
I have painted Bretonnia, Warriors of Chaos, Dwarves, Dark Elves, Empire, O&G, Wood Elves and Vampire Counts. Want to know my two absolute favorites that I had the most fun painting? My first two choices that I started with, since I loved the models and the fluff - Bretonnia and WoC - who cares if they are competitive? For 8th Bretonnia is weakened, but WoC got some boosts!
Paint the models and the background you love, because you will always love them, no matter how they rise and fall on the list over the years. If you jump into the most competitive army at the moment and the pendulum shifts, you will drop them faster than anything...
The biggest reason I picked my beloved High Elves is because I love their paint scheme. Before that, in the universe of 40k, I had chosen armies that were always painted to look dirty and dark, and having bright colors and crisp paint jobs is something I really like. Pick what you like to paint, then worry about how competitive they are.