As these are all trial installs I would have thought that Avast would have been more than happy to fix any install problem for you via their support. If they can't, do you really want to rely on their solution?
I use the free version of Avast on my home PCs and am very happy with it, but there are so many vendors out there in the business AV space and the most important criteria are visibility of computers and manageability.
If it doesn't work for you out of the box (we are all too busy) try something else. Scout out the testers like Virus Bulletin, AV Test or AV Comparatives to see what performs best. Though it seems some websites favour certain vendors with their test results.
We currently use Sophos which is very (excessively?) comprehensive in what you can do and covers more platforms than you new you had, though is not without it's foibles.
