I bought my brother an X5, and then got myself a 2215 the next month. I like my 2215 better -- but not by much. If I had the Axim, I wouldn't be feeling any remorse -- I really like it.
The only advantage the HP has is it's size+bluetooth.
Axim? -- already a boat-load of accessories, batteries, large user base, and updates posted by Dell. HP? Nada.
Also -- if you get bluetooth -- get the socket one -- fits into the SD slot completely -- no antenna!!!
Just my $0.02