Advent have a massive buff in firepower in their own gavitywell and have many powerful AOE attacks on thethie ships and starbase. Their tactical structures can buff shields and shield regen, can restore shields on single targets (if you were forcusing on the SB) and regenerate their AM.
If they were rebels their titan gets quite a firepower buff when their ships die, they can also attack you with a strong AOE attack.
The Advent Loyalist titan can mass-convert your ships and weaken your firepower by large amounts just by standing next to your fleet.
Your best bet is taking along 20+ Ogrovs and taking out the SB from outside it's range (Akkans increase your range to gains some additional safety distance) as quickly as possible and then take down the corvettes (rebel case) or the titan first (loyalist case).
Edit: One Titan being "better" than the others is suerly a thing of preference. I for one like the Advent Loyalist titan best for being able to debuff and take over fleets. The TEC and advent Rebel Titans are not my kind of thing, especially the Advent one. The TEC Rebel titan is too much of a loner for my tastes, ability wise.