The part that most likely help your genealogy is database matching with close relatives, who might have information that you don't. Predictions of relationships up to third cousins are very accurate and more remote ones can be useful. However, there will probably be cousin marriages, so that relationships will often be predicted closer than they really are.
The best strategy is to test at Ancestry ($99) and 23andMe ($99). You can then upload your 23andMe results to FTDNA's database ($89) and be in three databases. FTDNA is working on allowing Ancestry uploads, but it does not seem to be ready yet.
23andMe seems to have the best ethnicity test (Ancestry Composition). The Global, which gives European, Sub-Saharan, etc. is very accurate. However, sub-regional (e.g., within Europe)admixture is a more difficult problem