Depends also whether you (plan to) develop alone or have coders with PHP skills
I was starting to work with Smarty, but then when I experienced in another project how annoying the work with it is, I started to revert back to PHP
...I heard that PHP in it's beginning was something like templating engine anyway
What I basicly dislike is that anyway you have to copy tons of your variables into Smarty and then you have to learn and use syntax very similar, but much less powerful, as PHP
After you're finished you'll have code full of ifs and others code flow things anyway ... and you have to rely on that syntax and hope and be worried if what you want to achieve is possible with Smarty
So for me the only benefit might have been <?php echo $something?> => {$something} + $smarty->assign("something",...); so in the end it's not even shorter...
And I set ctrl+p to print <?php echo |?> (|= cursor placed after insertion) so...
under some circumstances I'd vote for PHP = I don't say templates don't have positives, just stating a different view
if you manage to bypass the need for some more complex things in PHP, than you don't need something that massive as Smarty - with all plugins it has 317kB...