4 man team help

You may choose a rogue and play around bombs with panda and enu as positioners/buffers and feca as extra damage/protection;
Or you can choose cra (str for example since your team lacks str) for a ranged approach as panda/feca/enu can all fight from distance;
Or you may choose str or str/int iop for raw damage, it might not be an ideal choice but it is sure one of the simplest and most straightforward classes, and sometimes a simple gameplay is a pleasure

As Vyyyyy has written above - Rogues are a popular choice to go alongside Pandawas, as they work well as a pair.
Using a Pandawa for tanking incoming damage, placement and to allow damage to deal more to enemies and using a damage rogue to set up bomb traplines.
In preparing to kill enemies from a number of locations together with the assistance of a Pandawa throwing and the Rogues bombot, bombs/bombglyphs and neutral bombs; Moving monsters onto bomb glyphs and deal large amounts of damage in a single hit.
Although this setup is only really needed to overcome endgame dungeons in PVM, that allow for this kind of play.

It all depends on what you want out of your team, you could try out some new classes before choosing a fourth and see what you feel comfortable playing and to enjoy long term.

Personally I run a Xelor, Eni, Panda and Feca as my main team, I used to have an Iop instead of a feca but in recent years as Xelors deal so much damage now I decided to swap Iop to a Feca. The reason being is because Rampart, Aegis and the melee and distance invulns help me loads at endgame, so incoming damage isn't overwhelming.
The glyph variant for Feca's as as for agility that increase melee damage when allies are on them is also fantastic and the strength one that boosts damage resistance. I recommend trying the different spells out when you are able, unless you are max level already.

An Eniripsa could be a great choice for a fourth, as they have damage improvement spell and can give ap and 1 mp. Although as you already have an Enu, they are great for healing and buffs. I play my Feca agility for the lock and because I benefit from the glyph damage together with my Xelors high damage.
I feel you'd benefit most from a high damager such as a Rogue, with a Int character holding a healing weapon as backup.

In addition, many choose to selectively build their Pandawas with high % Resistance, Lock and high Health Points. To allow them to take plenty of hits and lock monsters in place, so the monsters dont run off and kill bombs as an example.
It also allows for Pandawas to move the monsters around easier when the monsters are all in one place. 
Although this only really concerns specific endgame dungeons, such as fights in dimensions, which are some of the harder fights ingame currently.

Other popular choices are Elios with Iops or Srams with Fecas, as the spells allow good synergy between both pairs. Together with support damage, healing and general placement from any other two classes to make a team of four.