i have the exact opposite experience with my nexus 5.
my previous phone, lumia 920 used to get 2-3 bars in my house and depending on where you are, it can go to 0-1 as well. with my lumia 920, i couldn't even watch a short 3 minute youtube video without it buffering 10 times. with the nexus 5, i still get 2-3 bars at best, but those 2-3 bars are enough for me to watch a full 2 hour movie and it never buffs! i also average around 7mbps download compared to what i used to get with my lumia which was around 2 mbps at best. this is on att btw.
something i noticed with att signal strength. i have the att mobile hotspot as well and the funny thing is, when i have my nexus 5 and the mobile hotspot side-by-side, the hotspot always gets at least 1 bar more than the nexus 5. when i called and asked about the discrepancies between the two, the cust serv advisor had no clue (surprise).