Actually 7.7 should be smoother... the different between this device are the processor, lcd and 7.7 touchwiz is kind of got more option. but you can use better 3rd party launcher like adw/go launcher/etc... its work better on both device... other hardware kind of same...

if you are into custom firmware... both still lack of it... imho if your budget permit... go for 7.7... if not 7plus will do most job well...

btw depend on your hand size... 7.7 need to stretch a little bit if you got small hand...