Sust has a relatively high amount of PIP (post injection pain). It leaves a bigger lump on me that stays longer too (compared to test c). I wouldn't associate that with it not absorbing though... Plus from what I understand there is an even longer ester in sust than in test c and e etc. so I would assume (I'm no expert) that that slow release keeps the lump around a little longer.
At first glance, I thought sust sounded like the best option too, but it's really not, for the reasons we just talked about, and from what I understand to keep optimal levels of sust, you need to inject EOD... Which, from what we just discussed, is literally and figuratively, a pain in the ass.