Eu iria pessoalmente para o tmpfs, já que armazena arquivos na memória, em geral muito mais rápido.
Eu encontrei isto: link
tmpfs: is a filesystem which stores its files in RAM. This doesn't mean that the filesystem will eat all your RAM. Instead it takes only that amount it really needs. Usually only some MB are needed. If you'll use it, add a line like: none /tmp tmpfs size=64M,mode=1777 0 0 to your /etc/fstab. You can change the size to a value you like. If you think at some point that it is too less, you can use mount to increase the size: mount -t tmpfs tmpfs /tmp -o size=128M,mode=1777,remount. The size will be increased in place without deleting existing files.
ext2/3: You said in your question that you don't need any fancy features. However I would advice for using a journal. Because if you use ext2 and you have a quite large /tmp it would take some time for checking it. ext3 boots any many cases faster. Therefore I would suggest the use of journalling.
ext4, reiserfs etc.: Some software uses /tmp for storing large amounts of small files. So in some cases there are no more free blocks and the filesystem is full. ext4 and also reiserfs store files in a different way. So it could be a good choice to use those for your /tmp.
If your computer runs for a long time, it is a good idea to delete unused files in /tmp. tmpreaper is one solution which does that for you.
However my first choice would be using tmpfs.
EDIT: Desde que você não quer um diretório Lost + Found nem tmpfs, btrfs e reiserfs / reiser4 não tem um Lost + Found, afaik, talvez você queira usar um desses? Eu recomendaria o btrfs sobre o reiserfs / reiser4.
Comparação de sistemas de arquivos: link