Yaar sari confusion door ho jate hai!!
Poster is asking about that which engine is better EXI or VTI?
answer is VTi !! but y??
i'l tell u why 
yaar dekho.. as far as Civic 1.6 and 1.8 were compared!! Civic 1.6L is 127hp and Civic 1.8L is 140hp
khair civic 1.8 to beech mein hai he nai.. leave that 
Civic 1.6L is D16Y8 which is VTEC... VTEC has been discussed above in detail so no need to go over that!
Civic 1.5L is D15Z4 which is NON-VTEC... all the valves work! all the time! not much economic i guess*
yaar in simple words.. VTEC ka faida hai yeh ke jab ap 3000rpm ke under rehte ho to only 8valves open and when u rev above 3000rpm all 16v open.. and when u go beyond 5500rpm the valves open more and more efficietly (aka VTEC KICK)... this is much more economic than EXI only when u shift before ur rpm crosses 3000rpm..
and if u want to race or something.. the pedals under ur foot.. press it and ENJOY! Power plus Economy in a Smart Way
Honda all the way
VTEC (y)
1.6L vs. 1.5L
Definitly 1.6L VTi!!!