The simple answer is do all three
My first fantasy army was Lizardmen, and I enjoy them a lot. What I found after playing them was that there wasn't as much "tactical finesse", so to speak, as the units are much more straight forward. Combat blocks? S4, T4. Skirmishers? Skinks to go around and do their thing.
With Empire, it's T3 all over the place. Stat-wise, all the units are essentially the same. S3 T3, and it's only the armament that takes them into their roles. I find them to be the most rewarding army I've played from a tactical standpoint, as often you go up against units that look much nastier on paper compared to a lowly halberdier, and yet those halberdiers being led by a Warrior Priest (praise Sigmar) go and fight anyway. I enjoy it thoroughly.
Japehlio's suggestion about 40 halberdiers with a warrior priest is spot on. If you're having some trepidation about playing Empire, play that one unit and you might have your mind changed.
Yeah, other armies can do each individual phase better, but Empire can do everything. There's a lot of fun there. To take a look at your examples, Chaos has better lords/heroes, but no shooting. High Elves have great magic and some cool units, but can't horde up. Lizardmen have the awesome Slann, but they lack cheap cavalry and long range shooting. Brets have better cav, but worse infantry. Dwarves have better artillery, but Empire has enough to give them pause AND can move a whole lot better to boot. The best part is, you can have all of those elements in the same list! Figure a couple blocks of state troops, a level 4 wizard, a pair of cannons, and a unit of Knights and you have everything at your disposal, at really any playable point level. If you find you like one part more after playing for a bit, you can always just focus on that. If what you focused on ends up being boring, go the other direction. Endless fun!
I say get some new stuff, play with it, and don't give up on Empire just yet!
To answer your other question, 8th has been good to Empire. 7th was brutal, but in 8th I've had a lot of success against the whole slew of armies that are out there. I haven't played/bought the new shiny units yet (wizard mobiles/demigryphs) and I still do well with the army book.