TI-Basic, 130 bytes

Input N:If not(N:Goto 0:1+int(log(N→D:3+int(logBASE(N,16→H:0→F:1→I:While N>I and not(fPart(N/I:10I→I:F+1→F:End:log(D-1→L:1+D-F+(D-F>1):Ans+int(L)+(0≠fPart(L→S:(H>D)2(D>S)+(H≤D)(1+(H>S)→N:Lbl 0:N

Prints 0 for decimal, 1 for hex, 2 for scientific notation

TI-Basic, 130 bytes

Input N:If not(N:Goto 0:1+int(log(N→D:3+int(logBASE(N,16→H:0→F:1→I:While N>I and not(fPart(N/I:10I→I:F+1→F:End:log(D-1→L:1+D-F+(D-F>1):Ans+int(L)+(0≠fPart(L→S:(H>D)2(D>S)+(H≤D)(1+(H>S)→N:Lbl 0:N

Or, alternatively:

�N>θN>�0>1p��ND>3p�������BASEN+16H>0F>1I>�NlI@��N�I>10II>Fp1F>�>�Dq1L>1pDqFpDqFl1>rp�Lp0o�LS>HlD2DlSpHmD1pHlSN>�0>N

Or, in hex:

dc4e3eceb84e3ed7303e3170b1c04e04443e3370b1bbbcbbbfbbb642415345104e2b313604483e3004463e3104493ed14e6c4940b8ba4e83493e31304904493e46703104463ed43ec0447131044c3e317044714670104471466c31113e7270b14c117010306fba4c04533e10486c44113210446c53117010486d441110317010486c5311044e3ed6303e4e

Prints 0 for decimal, 1 for hex, 2 for scientific notation