Firstly, it's great that you're upgrading - your betta sure will enjoy the extra space :)
In my opinion, if you can afford the 10 gallon, go for the 10 gallon. As well as having the most space, it would also mean you'd be able to have tankmates if you wanted, 6 pygmy cories or so would do great in there.
Why not filter it though? Filters aren't expensive, and would mean you'd only have to do a 20% water change once a week and would generally make the tank a healthier environment. As for cycling, does your 2.5 gallon have a filter? If it does, and you get a filter for the new tank, simple put the filter media from the 2.5 into the new filter. If you have space left over, just put some new media in. This will maintain the bacteria your old tank had, and would eradicate the need for a cycle. You'd be able to add your betta as soon as everything settled, so possibly later that day. One other question, are you heating it? Bettas should ideally have temperatures that don't fall below 76
As for the glass-acrylic thing, I've had both. Where acrylic easily scratches, glass doesn't tend to, though glass is generally heavier than acrylic. I wouldn't worry about the choice between the two personally, it's unlikely to make a large difference to the tank from what I can see. Obviously, glass probably breaks easier (I've never tried), so that might be something to look out for