Another vote for the X3.
Anyway, the only way you can do solderless on a 1.6/1.6b is by using the spiderchip (which blows) or by using the xenium solderless adapter (which will work with both the x3 and the smartxx, as well as, of course, the xenium).
Honestly, the best way to go is to just solder it in. If you can't, then you probably know someone who can, and soldering is a much better solution than a solderless adapter.
i say smart XX all the way, xecuter, in my opinion, is over rated, like designer clothes, the exact same material as the clothes you'd find in charity shops, but cost stupid ammount for the label, i have 1.6b and have a smart xx V2 and id never trade it for an X3, unless a platinum case came with it...
The X3 and the SmartXX are the same price! While I do say get an X3, honestly all three should serve you fine, I just think that the X3 is the best.