Utilization looks at both revolving and installment accounts, but very differently.
The scoring gurus consider use of discretionary, revolving credit to be of much more predictive value than installment credit.
While no specific weightings are published, it is likely in the 90+% weighting for revolvging.
As for installment, you really dont have a "utilization" of installment credit, you have a % remaining of the original loan balance.
Knowing that any new installment will, by definition, have an almost 100% remaining balance after securing, you are not penalized for high % balances on installments.
For practical purposes, you can essentailly consider installment accts as not being part of your utilization of credit.
As for revolving, you are scored on three primary aspects.
First is overall % util of all (combined balances) / (combined CLs). That is the highest weighting. In that calculation, it doesnt matter which card(s) you divide a total monthly payment to, as the total payment, and thus new balance, would be the same.
FICO also looks at the % util of each individual acct, scores it separately, and then scores their combined affect. In that scoring, high % util accts take a proportionally higher score hit than lower util accts. Stated differently, a reduction of 10% in a very high util card will produce a higher score improvement than a 10% reduction in a relatively low % util card, so focus for scoring improvement should be on the highest % util cards.
Finally, FICO also looks at the % of cards that report any balance, as a percent of total cards. Two cards reporting a balance in a given month, and one reporting zero balance, would be 67% with balance. Percent of cards reporting a balance is the lowest weighted of the three revolving utilization sub-categories, so usually only becomes signfiicant when overall percent util gets low, and you enter fine-tweaking mode.
Starting Score: (FICO)(August 29, 2013) 502(EQ) 568(EX) 549(TU) 
