Already lvl 100 in Titan (and yes, it’s really powerful for most of my favorite teams). Is there any good hero class worth trying next? By good I mean that there are some teams specifically fit that hero and provide good strength and fun to play in PvP or Delve or Guild Event (at least for one of these).
Some of hero classes I’ve already play a little:
Archer lvl 43
Bard lvl 50
Dragonguard lvl 41
Frostmage lvl 15
Priest lvl 34
Sorcerer lvl 60
Thief lvl 48
Bard 
10 char
Frostmage is my pick.
At the very least, it has 50% mana start and Lightning Strike, but also has Immunity to Freeze, Freeze at the start of battle, Submerge allies on 4/5 match, and 20% magic damage reduction. All useful things.
Any good teams for Frostmage? I’ve played Frostmage for a while because a guildmate use it as major, but I feel it similar to Titan (50% mana start / lightning strike). Maybe in some freeze theme team?
Any good teams for Bard? I mainly used Bard before Titan, but I was completely fresh then 
You can try an Orb of Winter, (2nd troop), Queen Mab, Skadi team. Fey bonuses gives it magic bonuses to do a ton of damage. Otherwise, it typically works anywhere, its a pretty open ended hero to be used anywhere that could use a source of freezing the 1st slot (until fixed). (50% hero starts are great for that)
I do like to mess around with
Elemental Bow - Frost Mage
Green Slime
Infernus
Taloca
Unicorn Banner
It was supposed to be an Elemental hero at one point which would have made it much better, but its functional as it is currently.
THIEF (best class in the game)
Thanks! I don’t have Skadi for now but I’ll try to find some combination based on your suggestion.
People like the classes that offer a 50% mana start, those are all very good by default.
A few hero talents that make their hero stand out are Lightning Strike, ones that confer predictable status benefits like Barrier on color matches, and ones that summon replacement troops for dead allies.
Lightning Strike churns the board, and barrier-on-brown keeps your hero alive through ridiculous situations. Titan is considered objectively best by many because it offers both of those AND a fast mana start.
But some other classes like Bard, Archer, and Priest offer just enough utility beyond their talents people like to use them too.
I don’t agree with awryan on Thief yet, but I do know as a defensive class it’s very strong. Similarly, Dragonguard can be a pain to deal with.
So I guess I need to sit down and crunch which classes have the talents I like, but it’s so easy to just play Titan all the time I haven’t. Maybe if it didn’t cost gems to experiment I’d be more willing to branch out, but meh.
Runepriest is quite strong, it has the Stone Talent Tree which you already used on Titan, also the Guardian Tree that is one of my favorites because of Banishment on level 70 (Dispel all enemies on 4/5 matches) gives a bonus for Brown weapons which is great for the most basic teams with Mang in Raid/Invasions, unlocks Fortitude on level 100 and you hero is a Dwarf, to gain benefits from King Highforge.
The class could benefit more from decent Shields, but the Devs keep making very few usable with extra effects that requires a Boss in battle…
Priest + divine teams.
Or priest with dragon teams (that +yellow fits nicely with Divinia…)
Thief/assassin + skull rain teams (hunter mark anyone?).
Bard + (yellow) divines.
Etc.
I can’t agree more about this. Everytime I want to experiment more classes it’s a pain in the a**.