for arriving flights, provided it's same time for you to get home from LHR and LCY, LCY would always win for me.

I sometimes choose LHR over LCY for departing flights to use CCR / Lounges and have that "airport" feel to the trip but arriving, LCY is a breeze. In fact, the 9 mins mentioned by someone else can be easily beaten (though I tend to arrive domestic).

It's a short stroll to the terminal, bags are quick (if you check any in) and the DLR is 2-3 mins walk from the terminal. takes 22 mins to Bank.

there can be some holding at rush hour (just like LHR) but taxing takes 2 minutes, there are no "oh, there are no stairs" / "oh, we are at C gates" etc issues. it's nice, fast, easy and good.

so, go for LCY.

plus the 190 are great planes with extra leg room. both 170 and 190 are nice and new and 2-2 layout. food is better in CE (though the 2-2 layout in CE means no middle seat like on LHR flights). and if your international flight is the babybus (318 from JFK), go for it for sure.