I am familiar with Tanglewood, and if the TW 300 is of the Premier or Sundance series, then it would be a good guitar overall.
And most likely better in construction, and finish work, than the Martin Smith. (Both makes being British sales origins.)
Best, if it does have a solid top and not the laminate, veneer soundboard.
I've found that the Martin Smith line offers up consumer, student level or beginner entry level, introduction model lines that are really sub standard when compared to certain Tanglewood makes.
The real test of course, is the hands-on approach to ANY guitar in question. You have to try them out to discover what your real needs and expectations are for what you are looking for.
Then, only you will know which is the better guitar.
And, a Martin Smith is never a C.F. Martin.
Ever.