To be completely honest I don't think a pure jump army will be top tier. Sure you have the potential to smash IG Mexh but how about other mechanized armies carrying strong assault units? So you blow up a landraider full of thunder termies with your assault squad... Then they get pounded. The point being you need some long range anti tank.... This gives you options and forces your opponent to play more conservatively.
++ DREADNAUGHTS AS SUPPORT ++
Dreadnaughts in drop pods will help to provide some support up close and syncs with your assault units. If you want touse dreadnaughts then I think you'll need three to four. Sure some armies can nuke dreadnaughts but if you take more than two you can overload your opponent... The dreadnaughts are your hammer and your jump infantry is the anvil, or vice versa. The Furisio Librarian is the most powerful and should generally be your first choice. I would equip him with Wings of Sanguinius & Blood Lance. His inclusion in your army means that you don't need a Librarian which opens up another slot in your HQ choices. He is a beast in close combat and if you can keep him within range of a priest his S6 force weapon gives him the means to crush monsterous creatures without Eternal Warrior. He can also destroy tough units like Soul Grinders & other walkers if he has furious charge. The Furisio Librarian is also fairly impervious to Perils of the Warp which is another strong buff. Finally don't forget that Furisios are front armor 13 & WS6. My next choice would be a dreadnaught with multi-melta, heavy flamer & extra armor... Cheap for what you get, expendable and able to crack any tank at 1/2 range. If you are running Death Company then a Death Company dreadnaught would be my third choice. He has fleet and lots of attacks at WS5 plus furious charge built in. The Death Company dreadnaught is another cheap unit as well.
++ ASSAULT SQUADS ++
I think at this point it's important to remember that assault Marines are not close combat gods, not even with furious charge & rerolling missed hits. Sure they are good but never overestimate what they can do in assault. I played assault Marines with preferred enemy & furious charge with the PDF (Dante & Corbulo bubbles)... They were meh versus units like Plague Marines & Bloodletters, even when striking first at S5. If you play a jump heavy list then these guys will be your objective grabbers so you have to be careful with them. I think they are best at shooting. Like I said before I plan to run mine with a meltagun, flamer, infernus pistol & power fist. The flamer will be useful against guardsmen after you pop their transports.
++ STRONG ASSAULT UNITS ++
You are going to need a couple of strong assault units to fight the nasty stuff. Even Mephiston & Sanguinor need some support in close combat. Like I said Honor Guard & Sanguinary Guard will serve you well. If you take an Honor Guard then you only really need one Sanguinary Priest and this will save you some points. If you are thinking about running Mephiston then give the Sanguinor some consideration, while he is not quite as strong in close combat as Mephiston the Sanguinor can take a lot more punishment (obviously) plus he will buff one of your sergeants and you get the +1A bubble. I think in a few weeks when people learn how to counter Mephiston his popularity will start to decline. In my opinion Astorath, Recluisarchs & Chaplains are generally the best HQs as they help buff squads they join. The Furisio Librarian is the best choice for a psyker in your army.
++ LONG RANGE ANTI TANK ++
I also think if you were to field some landspeeders that would help out with the long range AT. I would go with a Typhoon with multi-melta. Your opponents will be less inclined to shoot at landspeeders if you've got some nasty close combat units up in their grill. Keep them back out of harms way and blast away.