The clear plastic is a good bet when you are raising seedlings..........rather than the green plastic, I would invest in a net cover as well............this enables you to grow on things a bit later in the season. The green plastic will only really do you a favour if you are raising plants early and in full sun
neither. glass is best and lasts longer.
Flowering rose.......I wouldn't disagree with you there...........however not everyone has the space for a glass house...........these little plastic jobs can be useful if you are short of space
I've had both covers - clear lets more light in as you can imagine but I have grown from seed many many plants in both clear and green without any hassle. The only difference is that the clear covers I've had seemed to rip quicker. I wouldn't bother spending loads of money on them as they only seem to last a year or two - or perhaps I am just unlucky!!
And although glass would be lovely, I too have a tiny tiny garden. It's also North facing with one tiny sunny spot.. I have to take the greenhouse down each year and put the garden bench there instead. Simply not enough room for both a bench and a greenhouse at the same time, so for me personally I am a big fan of those little plastic greenhouses!