i think you should determine which classes u enjoy playing the most. which ones suit your playstyle and create fun for you when you log in. Start there.
Which tank class works best with your playstyle and provides the best level of enjoyment and anticipation of playing. Your tank is almost always going to be your group driver. This will help you determine what other classes you want.
2nd thing to consider is your healer. these 2 set = win. Do you enjoy druids... are clerics your schtik. That shaman u played back in the day, did it float your boat. pick this class based on more than just heals, what other utilities can they offer. This site is full of information and thoughts on the healer class. dig through it and think what works best with how you enjoy the game.
next thing to consider is the buff/debuff/cc factor. what would you like, what content will you be doing, what is needed versus what would be enjoyed. tons to offer here and there is also utility offered by other classes (specifically DPS types). U want cc and slow and debuff and ridonkulous dps boost.. Bards can do all of that. not the best at some of it but absolutely viable in group content for all of it. You want debuffs and buffs and slows... beasts can also do these and add a stupid amount of dps and other types of utility. Don't forget that pet is basically a second tank with nice dps abd some " oh shit " factors added in. All of the dps classes add something besides dps. Some of them add things like ports and evacs, some add debuffs and buffs and cc. some add some sweet aura type effects. try them all out. even rangers can be nice. think of those cooldowns they have for your group... wow! You just cant wrong. its all about creating a group with synergy while keeping in mind your playstyle.
Dps is your 4th consideration, ( accepting the fact you already have slows and debuffs factored into your healer or factored into slot 3 dps spot ( bst/bard/other ) . This 4th spot you want to add in might not seem to be super important but this is the slot that will create the most enjoyment. It will be the guy that adds the frosting to the cake. There are all kinds of ways to go here. rogues, zerkers, monks etc. they all have the /autoskill that you can add in to make it easier. plus they have auras which can help. Some of them have the massive dmg spam factor. ya. i like that, i actually flip to my rogue sometimes and just watch a panel i isolated for his melee hits and crits and flurries lol. U had a rough day, watching this is like watching korean drama. its just relaxing ( it isn't the only dps class with this effect, is just the one i enjoy personally ) Possibly you prefer spells or ranged. whi knows, only you can find that out for yourself.
Thankfully EQ doesn't have a specific cookie cutter group like some games. u can mix and match till your hearts content. everything is viable in some way; some ways are just more fun. Don't be afraid to test configurations out and look in different directions. RG makes doing this so much more fun than the usual grind grind grind.. finally im high enough to see how this looks.... omg it sucks.. with RG, u can try out groups even at lower levels and see how they interact together with professinal level tools available and input from thoughtful, intuitive people.
Anyway. Not gonna push you in any direction. playing and figuring this out is where so much of the enjoyment comes from. If there's no valley, there's no peak. Test and fail and be unhappy from time to time. When things click.... ya baby, yah.
Very Best of luck to you on finding your fun