got an xperia z from coworker, loving it are the newer versions better? topic

For some reason this c6606 phone gets 4 bars better reception than any phone I have. It's a little beat up so I'm thinking about getting the newer versions (are they better?) How easy is it to install ROMs. I've rooted it and the only thing I don't like is the tmobile built in tether program keeps telling me I need to get the upgrade to get hotspot working.