What are the best water filters/ companies for the kitchen faucet and shower that are easy to place (do not require a plumber/ are NOT under the sink)? 

I primarily concentrate on comprehensive whole home solutions and I am not as well-versed in DIY systems. Nevertheless, a system such as iSpring, featuring a multi-stage activated carbon block filter and third-party testing to comply with NSF/ANSI Standards, is generally considered a reliable model. 

When considering a shower filter, I would recommend seeking similar qualities. Look for a system that incorporates a multi-stage filtration process and has undergone third-party testing to meet recognized standards, ensuring its reliability and effectiveness.