hi ident...
i have a lot of time instructing in both but i was cessna driver before piper.
you willl find this was debated before on prune .a dozen different pilots will give you a dozen different reasons why one likes a 172 and another a PA28...thats just a fact of life...like one man likes a girl another does not...and every now and again two will like the same girl..!!! .thats true of aeroplanes also...and the reasons can be varied...like i never liked having no door at my side... i want to be first out..!!!
my standard passanger briefing in the PA28 included how to open the door...exit towards the rear and included...''and do'nt slow down or look back 'cause you'll get run down by me as i'll be moving faster than you...''!
they are both nice planes and fun to fly. neither will set the world on fire with speed but very safe.
the 172 version i flew was the 145 continental six cylinder one as brooklands has pointed out ..but now its diesel...and very good and economical ( 50% power...80 knots...3.5 imperial gallons of JET A1 per hour ).
for short fields ( do'nt recall what the books say)...but for me the 172 without a shadow of a doubt.
as you say, finish the check out and then do the 172 . give them both a chance and then join the club...as you will then have made up your own mind and you can step to one side of the line with whichever group of drivers you identify with...and believe me you will...!!!
good luck and safe flying...
the dean.