I'd almost be inclined to say the Tray Loader, as the plastic frame inside the Slot Loaders likes to crack and flake with age. If the 333MHz if mint as well, it's an even better deal. It won't be as quick as the Slot Loader DV however. I would think 160MB of memory would cut it for what you want to do with it. I think most machines of that era had between 64MB and 128MB standard (although the early iMacs only had 32MB, so chances are someone stuck a 128MB extra module into yours), so you should have some room to move.

You can't however add AirPort to the Tray Loader, and the hard drive needs to be split into two partitions for Mac OS X. For OS 9 this isn't a problem. Both machines use ATA drives and are capped at 128GB maximum.

Of course, each model has its pros and cons, and ultimately it's up to you at the end of the day.