In my experience DMing and playing, being one dimensional should not be the bad word that it is often made out as. Each core class has defenses that they will tend to be good at. The paladin has a +1 boost to all three, but trying to 'keep up' with all three will waste resources and leave you with fewer options.
Up defenses in ways that are easy until you go paragon at least. A heavy shield gives you +2 Ref and AC, a good choice for paladins and fighters.
Fighters, paladin's and warlocks all have powers with boosts on a high Con, and wizards, rogues, and rangers have powers with benefits to from intelligence and other abilities.
For your paladin, if you want a defense tank, consider the heavy shield, and a high Con. if you start out with a 16 con, and focus on it, by 30th level as the demi-god you have con 26 (+8) level (+15) human (+1), class (+1), magic (+6), base (10) = fort 41 even without a feat. Consider multi-class feats to fighter instead of the defense boost feats. The fighter has a number of powers that benefit from high con on damage with as a hammer which you can use with your shield. So to does the warlock, and some of those use Con to hit as well. I like the warlock power shroud of black steel for the multi -class paladin. the defense boost is nice, and even in plate armor the speed penalty is negligable. consider mounted combat as a tactic to negate it. Then your feats will have been used to get you other benefits, and still take advantage of your high con. Other classes have abilities that they tend to naturally focus on. Remeber after that first round, it won't matter how high Orcus has to hit if he's prone, stunned, flanked, and blinded etc. which a whole party of 30th level characters ought to be able to dish out. If you each uncork your dailies right away, (which I imagine you would), at that level, if each member of the party isn't uncorking coupe de gras or at least multiple crits with the negative conditions being imposed with the damage, you're in real trouble against a level appropriate solo.