In terms of share prices, 2015 has not been a banner year for this country's large incumbent banks. For the most part, they have traded flat or somewhat down since the beginning of the year, generally trailing the S&P 500 index.

Part of the problem is that these are massive, sprawling enterprises involved in a great many businesses, and size can drag down performance. Considering this, investors have been taking a closer look at smaller banking groups, as the better ones are (ideally) more streamlined and efficient, and hold greater potential as investments.

Source: Gerald England.

We asked three Fools to pick one regional banking stock apiece they feel is worthy of serious investor consideration. Here are their suggestions.

Sean Williams: If you're thinking of buying a regional bank stock, consider Umpqua Holdings (UMPQ), a retail and commercial lender operating out of the Pacific Northwest.

Like most banks in the region, Umpqua struggled to right the ship for years after property values tumbled and loan delinquencies rose. However, instead of getting into the fetal position and hoping for the best, Umpqua's management took a more proactive approach and announced it would purchase Sterling Financial two years ago for $2 billion.

This more than doubled Umpqua's deposits, boosted its retail branch locations by around 100%, nearly doubled its total assets, and should ultimately lower its expenses... although, not surprisingly, there have been merger-related costs and hiccups that have caused Umpqua's stock to trade essentially flat for two years now.

But Umpqua now has a much larger presence in the region. This is critical to drawing in new customers, growing the deposit base, and keeping a community feel while also building rapport that can lead to lucrative retail and commercial loans.

Speaking of loans, we're also witnessing a majority of Umpqua's bread and butter business heading in the right direction. Net annualized loan growth sat at 10.9% in Q2, while annualized net charge-offs for loans and leases remained unchanged at 0.17%. Non-performing loans and leases also fell from the prior-year period.

Although net interest margins declined, and deposits dipped $77.5 million due to what management referred to as "tax-dependent withdrawals," the key components we'd look for in a healthy bank -- such as return on average assets and efficiency ratio -- are heading in the right direction.

Essentially trading at book value and a forward P/E of 13, I'd suggest that nothing short of another real estate bubble can stop Umpqua's long-term momentum.

Jordan Wathen: Keep this one on your watchlist: BOK Financial (BOKF -1.38%). A $31 billion bank by assets, it sits right in the middle of the oil patch, doing the bulk of its lending in its home state of Oklahoma, as well as Texas. 

While its exposure to energy may be a warning sign, I tend to think oil price concerns are mostly overblown. BOK Financial has been a consistently strong underwriter, charging off only 1.14% of its loans at the depth of the financial crisis in 2009. In the years since, charge-offs have been modest (negative in 2014) and totaled 0.02% of loans so far in 2015.
 
Of its roughly $15 billion loan portfolio, $2.9 billion is invested in energy loans. Safer, lower-yielding securities make up the remainder of its balance sheet assets.
 
BOK Financial noted recently that it stress tests its energy loans with base line assumptions of $40 oil and $2.50 natural gas, both well below current market prices. Loans backed by oil and gas properties are also evaluated twice each year by in-house petroleum engineers, mitigating risk. Furthermore, BOK Financial is more diversified than most banks, generating roughly half of its revenue from net interest income and the other half from fees.
 
That insiders own 69% of the company also gives me confidence that it isn't taking undue risks. Continued worries about the energy industry could give investors the opportunity to buy a well-run bank at a very good price.

Eric Volkman: If you're going to invest in a regional bank, its region should be home to a thumping economy. That's very much the case with SVB Financial Group (SIVB.Q), one of the top lenders in the hottest tech neighborhood on the planet.

SVB Financial Group is the holding company of Silicon Valley Bank. As the latter name would suggest, the bank concentrates on the smaller, often early-stage companies associated with the region. Although that sounds precarious and high risk, the lender provides its services not only to these types of enterprises, but also the venture capital operators and other investors financing them.

It's a great business to be involved in, considering the local scene is always in need of capital. The bank operates a solid business model, making its coin by both traditional lending and fees for its services. It's managed to grow the take from both over the years, with both interest and non-interest income rising sharply over the past half-decade.

Meanwhile, the company's loan book has nearly tripled over that span of time, and its expenses have been tamed -- the annual efficiency ratio figure has dropped steadily, from nearly 70% in 2010 to last year's 57%.