The title say it all ... except to clarify:
* 'spiral' includes edge-on and lenticulars
Follow-on question: which NGC spiral is the largest, physically?
Clarifications:
* not counting the tidal tails of spirals in mergers
* 'largest, physically', as a metric, should be consistent (i.e./e.g. NGC ABCD may be the largest, physically as measured by the scale length of its disk (exponential fit), but NGC EFGH by the furthest-from-the-nucleus 21 cm detected emission; pick a metric, and use it consistently).
As always, the how trumps the what; "how did you find the answer?" is more important than "what is the answer?"