I recommend you go
here to read up a bit. It has a nice description of all the factions, with a general discussion about strenths and weaknesses.
As for your super units...
Warlord Titan
Strengths: Ridiculous number of shields and stucture points. Lots of very powerful guns.
Weaknesses: No model exists for it, so you'll have to make it yourself, and it's expensive. For its points cost I could likely put together a force that would take it down. Read up on dakka's own
Titan Tactica for more information.
Baneblade
Strengths: Jack of all trades super heavy. It can do anything decently, and it's thick skinned. It also does not suffer from the 'one huge gun' syndrom of other Imperial superheavies.
Weaknesses: Expensive again, but at least there's a plastic kit for it. Once again, with the points it costs I could come up with a tank hunter force that could bring it down. Read dakka's
Super Heavy Tactica for more information.
Thunderhawk
Strengths: Flyer so fast as all hell, and can pcak a heavy punch, not to mention carry a ton of Marines and other equipment.
Weaknesses: THink skinned compared to other superheavies, and lots of
AA fire will bring it down sooner or later
TO be honest, there's not really a whole lot to be said for the factions. The strength and weaknessed of each army are so deep it'd take ages to spell them out.