Thief is by far the best compared to Assassin simply because extra bonus action.
Also yes, agreed with OneTrueNobody, a character isn't defined by how high the damage he can deal in one turn, which still pretty nice, but there is so much stuff you can do outside of fights that pretty much having a Rogue will beneficial.
I am level 5 with my whole group: Main (Rogue), Shadowheart (Cleric), Gale (Sorc), Lae'zel (Fighter).
I want to fight melee with my rogue, because this is my pure understanding of that class.
Maybe, I am playing it wrong, but after my initial sneak attack it feels pretty dumb to stay around and just hit with a normal attack next round - it feels pretty unsatisfying to be honest.
In my opinion, ranged damage / ranged enemies is pretty strong - currently, I am looking for some protection against ranged damage, because most of the combat (balanced difficulty) against my group has devastating outcomes, when 3-4 ranged enemies are taking actions (just want to mention the Duergar Ship Battle). I had to reload this fight 7-8 times to defeat all the dwarfs.
PS: Sorry, I'm from Germany. My game language is German, so my text could contain some wrong descriptions.
You'd want to play thief rogue, you have 2 bonus actions, which means you can disengage and then look for deadspot to back into hiding and then sneak attack again.
You can sneak attack at every turn. Given the right condition. Condition which you must create for yourself.
Pay attention to vision cone and terrain, sometimes you don't even need to go to hide to commit sneak attack, if you make the enemy on disadvantage, you can strike sneak attack without hiding, this is where your choice of companion is important too.
