I recently went through this decision myself. Something I was told is you should be able to consistently stand up/catch waves on your current board before you move to a "harder" board. So by this advice you start on a foamie. I went for a cheap ($50) slightly used foamie. Of my 5 friends who also just started we split 2/3 foamie/fiber. I think the 3 that went for a fiberglass board (used ~$100-250) are happier. I'll be buying a fiber board soon. Now that that anecdote is out of the way onto advice.
Things I was told to consider:
- Are you sure you will continue with surfing? If the lessons are enjoyable and you are fairly sure then just make the investment.
- Foam boards are easier to take care of. If you bang it in your garage, while walking, etc then you aren't going to have an issue. The same can't be said for a fiberglass board
- Foam boards hurt less if you fall on them. While you are learning this can be nice
- Foam boards hurt others less if you hit them. If you are having trouble controlling yourself while surfing it might be good to buy a foam board for the sake of surfers around you
- Fiberglass boards are going to be faster. This means easier to paddle onto a wave.
- Fiberglass board is what you will eventually buy, so buying one at the start allows for longer progression on the same board
- Regardless of board type, pick a longish board (7-8ft) with a more rounded nose (won't nosedive into waves as often while learning)
- Volume matersmatters. The more volume the more stable it will be (in general). Most boards have a number of Liters of volume
A lot of places(/friends) let you demo used fiber boards for cheap. Some will even put the rental cost to buying a board. If possible, try demoing one and if you are able to get up consistently then just buy a fiberglass board.